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Our genes are very important for the development of mental disorders-including ADHD, where genetic factors capture up to 75% of the risk. Until now, the search for these genes had yet to deliver clear results.   In the 1990s, many of us were searching for genes that increased the risk for ADHD because we know from twin studies that ADHD had a robust genetic component.  Because I realized that solving this problem required many DNA samples from people with and without ADHD, I created the ADHD Molecular Genetics Network, funded by the US NIMH.  We later joined forces with the Psychiatric Genomics Consortium (PTC) and the Danish psych group, which had access to many samples.  
The result is a study of over 20,000 people with ADHD and 35,000 who do not suffer from it - finding twelve locations (loci) where people with a particular genetic variant have an increased risk of ADHD compared to those who do not have the variant.  The results of the study have just been published in the scientific journal Nature Genetics, https://www.nature.com/articles/s41588-018-0269-7.
These genetic discoveries provide new insights into the biology behind developing ADHD. For example, some genes have significance for how brain cells communicate with each other, while others are important for cognitive functions such as language and learning.
Our study used the genome-wide association study (GWAS)methodology because it allowed us to discover genetic loci anywhere on the genome.  The method assays DNA variants throughout the genome and determines which variants are more common among ADHDvs. control participants.  It also allowed for the discovery of loci having very small effects.  That feature was essential because prior work suggested that, except for very rare cases, ADHD risk loci would individually have small effects.
The main findings are:

A) we found 12 loci on the genome that we can be certain harbor DNA risk variants for ADHD.  None of these loci were traditional candidate genes' for ADHD, i.e., genes involved in regulating neurotransmission systems that are affected by ADHD medications.  Instead, these genes seem to be involved in the development of brain circuits.  
B) we found a significant polygenic etiology in our data, which means that there must be many loci(perhaps thousands) having variants that increase the risk for ADHD.  We will need to collect a much larger sample to find out which specific loci are involved;

We also compared the new results with those from a genetic study of continuous measures of ADHD symptoms in the general population. We found that the same genetic variants that give rise to an ADHD diagnosis also affect inattention and impulsivity in the general population.  This supports prior clinical research suggesting that, like hypertension and hypercholesteremia, ADHD is a continuous trait in the population.  These genetic data now show that the genetic susceptibility to ADHD is also a quantitative trait comprised of many, perhaps thousands, of DNA variants
The study also examined the genetic overlap with other disorders and traits in analyses that ask the questions: Do genetic risk variants for ADHD increase or decrease the likelihood a person will express other traits and disorders.   These analyses found a strong negative genetic correlation between ADHD and education. This tells us that many of the genetic variants which increase the risk for ADHD also make it more likely that a person will perform poorly in educational settings. The study also found a positive correlation between ADHD and obesity, increased BMI, and type-2 diabetes, which is to say that variants that increase the risk of ADHD also increase the risk of overweight and type-2 diabetes in the population. This work has laid the foundation for future work that will clarify how genetic risks combine with environmental risks to cause ADHD.  When the pieces of that puzzle come together, researchers will be able to improve the diagnosis and treatment of ADHD.

An Israeli team compared eating habits and body mass index(BMI) in adults with and without ADHD. They recruited 60 students from Hebrew University in Jerusalem between 20 and 30 years old. To avoid bias due to particular diets, the authors excluded vegetarians and vegans, as well as persons with chronic diseases that require altered diets, such as diabetes, inflammatory bowel diseases, and chronic kidney disease. Twenty-nine of the participants had been diagnosed with ADHD.
All participants filled out the Food Frequency Questionnaire, a semi-quantitative scale querying about 119 food items. Based on World Health Organization guidelines, it distinguished between "healthy" items (such as vegetables, fruits, whole grains, and minimally processed foods)and "unhealthy" ones (such as cookies, processed meats, and other processed foods). The data obtained from the questionnaires were linked to a nutrient database to estimate daily nutrient intake. BMI was calculated from heights and weights reported by the students.
No significant differences were found between the two groups for servings, calories, fats, carbohydrates, and proteins. Yet, the ratio of healthy to unhealthy portions was significantly higher among controls than among those with ADHD. Those without ADHD consumed about a quarter more servings of healthy food and about a quarter fewer servings of unhealthy food.
On average, BMI levels were about 13 percent higher in participants with ADHD than among those without, meaning they were significantly more likely to be overweight. This finding is consistent with many prior studies.
The authors concluded, "Although participants in both groups consumed similar amounts of servings, calories, and nutrients, students with ADHD reported eating lower amounts of healthy food and higher amounts of unhealthy food. The results suggest that ADHD is not associated with general overeating, but with a biased proportion of unhealthy versus healthy food consumption."
They also recognized limitations to their study. One was a relatively small sample size and the fact that all participants were recruited from a single university. Another is that they did not try to fully evaluate the effects of medication, other than to note the absence of significant differences in food choices between those who used medication regularly and those who used it only occasionally. An unrecognized limitation was the exclusive reliance on self-reporting, both for food consumption, weight, and height.
Despite these limitations, this study is an important first step toward understanding the eating habits of people with ADHD.  It suggests to me that those treating ADHD should promote healthy lifestyles, as that should reduce ADHD's known risks of obesity and adverse medical outcomes.

All Swedish residents have their health records tracked through unique personal identity numbers. That makes it possible to identify psychiatric and medical disorders with great accuracy across an entire population, in this case encompassing more than five and a half million adults aged 18 to 64. A subgroup of more than 1.6 million persons between the ages of 50 and 64 enabled a separate examination of disorders in older adults.
Slightly over one percent of the entire population (about 61,000) was diagnosed with ADHD at some point as an adult. Individuals with ADHD were nine times as likely to suffer from depression as were adults not diagnosed with ADHD. They were also more than nine times as likely to suffer from anxiety or a substance use disorder, and twenty times as likely to be diagnosed with bipolar disorder.  These findings are very consistent with reports from clinical samples in the USA and Europe.
Adults with ADHD also had elevated levels of metabolic disorders, being almost twice as likely to have high blood pressure, and more than twice as likely to have type 2 diabetes. Persons with ADHD but without psychiatric comorbidities were also almost twice as likely to have high blood pressure, and more than twice as likely to have type2 diabetes.
Similar patterns were found in men and women with ADHD, although comorbid depression, bipolar disorder, and anxiety were moderately more prevalent in females than in males, whereas substance use disorder, type 2 diabetes, and hypertension were more prevalent in males than in females.
ADHD was less than a third as prevalent in the over-50 population as in the general adult population. Nevertheless, individuals in this older group with ADHD were twelve times as likely to suffer from depression, anxiety, or substance use disorders, and more than 23 times as likely to be diagnosed with bipolar disorder as their non-ADHD peers. They were also 63% more likely to have high blood pressure, and 72% more likely to have type 2 diabetes.
The authors noted, "Although the mechanisms underlying these associations are not well understood, we know from both epidemiologic and molecular genetic studies that a shared genetic predisposition might account for the coexistence of two or more psychiatric conditions. In addition, individuals with ADHD may experience increased difficulties as the demands of life increase, which may contribute to the development of depression and anxiety." As for associations with hypertension and type 2 diabetes, these "might reflect health risk behaviors among adult patients with comorbid ADHD in addition to a shared biological substrate. As others have noted, inattention, disinhibition, and disorganization associated with ADHD could make it difficult for patients to adhere to treatment regimens for metabolic disorders." They concluded that "Clinicians should remain vigilant for a wide range of psychiatric and metabolic problems in ADHD affected adults of all ages and both sexes."

The CDC recently reported that ADHD medication use in women ages 15 to 44 increased from 0.9 percent to 4 percent from 2003 to 2015.  The most commonly used medications were formulations of amphetamine or methylphenidate.  

This increase in treatment for ADHD suggests that educational programs such as adhdinadults.com have been effective in teaching clinicians how to identify and treat the disorder.   The 4 percent rate reported by the CDC is encouraging because it is close to what Ron Kessler and colleagues reported as the prevalence of adult ADHD in the population.   CDC correctly points out that little is known about the effects of ADHD medications on pregnancies. Thus, caution is warranted.

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Oei et al.'s review of amphetamines concluded: "There is little evidence of amphetamine-induced neurotoxicity and long-term neurodevelopmental impact, as data is scarce and difficult to extricate from the influence of other factors associated with children living in households where one or more parent uses drugs in terms of poverty and neglect. ... We suggest that exposed children may be at risk of ongoing developmental and behavioral impediment, and recommend that efforts be made to improve early detection of perinatal exposure and to increase the provision of early intervention services for affected children and their families"

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Bolea-Alamanac et al.'s review of methylphenidate effects concluded: "There is a paucity of data regarding the use of methylphenidate in pregnancy and further studies are required. Although the default medical position is to interrupt any non-essential pharmacological treatment during pregnancy and lactation, in ADHD this may present a significant risk. Doctors need to evaluate each case carefully before interrupting treatment." These words of caution should be heeded by clinicians caring for women of reproductive age.

A team of U.S. endocrinologists recently published the results of a meta-analysis examining a possible association between bisphenol A(BPA) and childhood ADHD. BPA is used in a variety of consumer products, including plastic bottles for food and drink, epoxy resins used to line cans of food, dental sealants, and the thermal receipts issued by stores.
A review of the literature found 29 rodent studies, but only three with humans. The human studies were too different from each other to be suitable for meta-analysis. One found no association between prenatal exposure and ADHD. A second found prenatal BPA exposure to be associated with teacher-reported hyperactivity in 4-year-old boys, but not girls. The third found is to be associated with hyperactivity scores in 3-year-old girls.
As the authors note, "Often, there is little human data available, particularly in the environmental toxicology/health fields, due to the time and expense of conducting epidemiological studies and the ethical barriers for human-controlled trials that involve human exposure to potentially hazardous chemicals. Thus, it is important to have methods for using animal data to inform human health hazard conclusions; indeed, animal models are traditionally used to study human health."
Twelve of the mice and rat studies, with a total of 709 rodents, were suitable for meta-analysis.
Overall these pointed to a tiny SMD effect size of 0.09, but it was not significant, with the odds of such a result being obtained by chance being almost one in four (p = 0.237). But when results from the 356 males and353 females were looked at separately, a significant sex difference emerged. There was essentially no effect on female rodents, with an effect size of -0.07and a 95% confidence interval of -0.27 to 0.14, widely spanning the zero mark, rendering the result statistically non-significant. Among male rodents, however, there was a small but statistically significant effect size (0.24), with a 95%confidence interval from 0.04 to 0.45. The odds of obtaining this outcome by chance were only one in 50 (p = .02).
This result must be viewed with caution, as rodent physiology often differs substantially from that of humans. The authors, therefore, conclude, "early BPA exposure is associated with a presumed hazard of hyperactivity in humans. Our conclusion is based on 'moderate' levels of evidence for the human and 'high' levels of evidence for animal literature."

A Norwegian team based at the University of Bergen recently performed a population study using the country's detailed national health registries. With records from more than two and a half million Norwegians, the team examined what, if any, associations could be found between ADHD and nine autoimmune diseases: ankylosing spondylitis, Crohn's disease, iridocyclitis, multiple sclerosis, psoriasis, rheumatoid arthritis, systemic lupus erythematosus, type 1 diabetes, and ulcerative colitis.

After adjusting for age and maternal education, the team found no association between ADHD and five of the nine autoimmune disorders: type 1 diabetes, rheumatoid arthritis, iridocyclitis, systemic lupus erythematosus, and multiple sclerosis. In the case of ankylosing spondylitis, it found no association with males with ADHD, but a negative association with females. Females with ADHD were less likely to have ankylosing spondylitis. The adjusted odds ratio (AOR) was 0.56 (95% CI 0.32-0.96).

Positive associations were found for only three autoimmune diseases. The strongest was for psoriasis, with adjusted odds ratios of 1.6(95% CI 1.5-1.7) for females and 1.3 (95% CI 1.2-1.4) for males. When further adjusted for education, smoking, and body mass index (BMI), however, the adjusted odds ratio for females with ADHD dropped to 1.3 (95% CI 1.0-1.6).

The second-strongest association was with Crohn's disease. But here it was only among women. The odds ratio, in this case, was 1.4 (95% CI 1.2-1.8). Males with ADHD were less likely to have Crohn's disease, with an odds ratio of 0.71 (95% CI 0.54-0.92).

Finally, females with ADHD were slightly more likely to have ulcerative colitis, with a barely significant odds ratio of 1.3 (95% CI 1.1-1.5), while no such association was found for males with ADHD, whose odds ratio was a statistically non-significant 0.9.

Given the large sample size of over two and a half million, this is no underpowered study. It found no association between ADHD and the generic category of autoimmune disorders. Furthermore, it is a stretch to argue that there are any clear and clinically meaningful links between ADHD and any of the specific disorders that were analyzed in this study. The small and often opposite effect sizes may simply reflect limitations with the data (presumed autoimmune disorders were identified based on drugs prescribed), or other unidentified confounding factors.

Several meta-analyses have assessed this question by computing the standardized mean difference or SMD statistic.  The SMD is a measure that allows us to compare different studies. For context, the effect of stimulant medication for treating ADHD is about 0.9.  SMDs less than 0.3 are considered low, between 0.3 to 0.6 medium, and anything greater than high.
A 2004 meta-analysis by Schab and Trinh combined the results of fifteen studies with a total of 219 participants and found a small association(SMD = .28, 95% CI .08-.49) between consumption of artificial food colors by children and increased hyperactivity. Excluding the smallest and lowest quality studies further reduced the SMD to .21, and a lower confidence limit of .007 also made it barely statistically significant. Publication bias was indicated by an asymmetric funnel plot. No effort was made to correct the bias.
A 2012 meta-analysis by Nigg et al. combined twenty studies with a total of 794 participants and again found a small effect size (SMD =.18, 95% CI .08-.29). It likewise found evidence of publication bias. Correcting for the bias led to a tiny effect size at the outer margin of statistical significance (SMD = .12, 95% CI .01-.23). Restricting the pool to eleven high-quality studies with 619 participants led to a similarly tiny effect size that fell just outside the 95% confidence interval (SMD = .13, CI =0-.25, p = .053). The authors concluded, "Overall, a mixed conclusion must be drawn. Although the evidence is too weak to justify action recommendations absent a strong precautionary stance, it is too substantial to dismiss."
In 2013 a European ADHD Guidelines Group consisting of 21 researchers (Sonuga-Barke et al.) performed a meta-analysis of eight studies involving 294 participants that examined the efficacy of excluding artificial colors from the diets of children and adolescents as a treatment for ADHD. It found a small-to-medium effect size (SMD = .32, 95% CI .06-.58), with less than one in fifty probability that such a result would occur by chance. Yet "Restricting the probably blinded assessment analysis to the four no/low medication trials reduced the standardized mean difference (0.32) to non-significant levels (95%CI=-0.13, 0.77)."
On balance, the research to date suggests a small effect of artificial food colors in aggravating symptoms of hyperactivity in children, and a small beneficial effect of excluding these substances from the diets of children and adolescents, but the evidence is not very robust. More studies with greater numbers of participants, and better control for the effects of ADHD medications, will be required for a more definitive finding.
In the meantime, given that artificial food colors are not an essential part of the diet, parents should consider excluding them from their children's meals, since doing so is risk-free, and the cost (reading labels) negligible.

A study conducted at Auburn University in Alabama recruited 54 college students to address this question. All had previously been diagnosed with ADHD. All lived independently, and all were taking prescribed ADHD medication. Students with severe comorbid psychiatric conditions were excluded. Three students dropped out, leaving a final sample size of 51.
Each student completed a total of four half-hour assessments, scheduled at monthly intervals. At each first assessment, researchers counted the participant's ADHD medication pills and transferred them to an electronic monitoring bottle-a bottle with a microchip sensor in the cap that automatically tracks the date and time of every opening. This enabled them to compare students' subjective estimates at subsequent assessments with the objective evidence from pill counts and the data output from the electronic monitoring bottles.
Overall, students reported missing about one in four (25 percent) of their prescribed doses. But the objective measures showed they were skipping closer to half their doses. According to pill counts, they were missing 40 percent of their doses, and according to the electronic monitoring bottles, 43 percent. The odds of obtaining such a result due to chance with a sample of size were less than one in a hundred (p < 0.01).
In other words, college students with ADHD significantly overestimate their adherence rates to their medications. The authors concluded, "without additional strategies in place, expecting adolescents and young adults with ADHD to remember a daily task that requires no more than a few seconds to accomplish, such as medication taking, is unrealistic. They suggest using smartphone reminder applications ("apps") and text messaging services.
The authors caution that this was the first such study and that it had a small sample size. Moreover, the study was not randomized. Students responded to advertisements posted on campus, and thus self-selected.
Pending the outcome of larger studies with randomization, the authors suggest that wherever possible, prescribing physicians adopt objective measures of medication adherence, as an aid in ensuring greater efficacy of treatment.

Roughly one in thirty adult women have ADHD. Research results indicate that psychostimulants (methylphenidate and amphetamines) offer the most effective course of treatment in most instances. But during pregnancy, such treatment also exposes the fetus to these drugs. Several studies have set out to determine whether such exposure is harmful.

The largest comparison was 5,571 infants exposed to amphetamines and 2,072 exposed to methylphenidate with unexposed infants. It found no increased risks for adverse outcomes due to amphetamine or methylphenidate exposures. Another study studied 3,331 infants exposed to amphetamines, 1,515 exposed to methylphenidate, and 453 to atomoxetine. Comparing these infants to unexposed infants, it found a slightly increased risk of preeclampsia, with an adjusted risk ratio of 1.29 (95% CI 1.11-1.49), but no statistically significant effect for placental abruption, small gestational age, and preterm birth. When assessing the two stimulants, amphetamine, and methylphenidate, together, it found a small increased risk of preterm birth, with an adjusted risk ratio of 1.3 (95% CI 1.10-1.55). There was a statistically significant effect for preeclampsia, placental abruption, or small gestational age. Atomoxetine use was free of any indication of increased risk.

Another study involving 1,591 infants exposed to ADHD medication (mostly methylphenidate) during pregnancy, reported increased risks associated with exposure. The adjusted odds ratio for admission to a neonatal intensive care unit was 1.5 (95% CI 1.3-1.7), and for the central nervous system, disorders were 1.9 (95% CI 1.1-3.1). There was no increased risk for congenital malformations or perinatal death.

Six studies focused on methylphenidate exposure. Two, with a combined total of 402 exposed infants, found no increased risk for malformations. Another, with 208 exposed infants, found a slightly greater risk of cardiovascular malformations, but it was not statistically significant. A fourth, with 186 exposed infants, found no increased risk of malformations but did find a higher rate of miscarriage, with an adjusted hazard ratio of 1.98(95% CI 1.23-3.20). A fifth, with 480 exposed infants, also found a higher rate of miscarriage, with an odds ratio of 2.07 (95% CI 1.51-2.84). But although the sixth, with 382 exposed infants, likewise found an increased risk of miscarriage (adjusted relative risk 1.55 with 95% CI1.03-2.06), it also found an identical risk for women with ADHD who were not on medication during their pregnancies (adjusted relative risk 1.56with 95% CI 1.11-2.20). That finding suggests that all women with ADHD have a higher risk of miscarriage, and that methylphenidate exposure is not the causal factor.

Summing up, while some studies have shown increased adverse effects among infants exposed to maternal ADHD medications, most have not. There are indications that higher rates of miscarriage are associated with maternal ADHD rather than fetal exposure to psychostimulant medications. One study did find a small increased risk of central nervous system disorders and admission to a neonatal intensive care unit. But, again, we do not know whether that was due to exposure to psychostimulant medication or associated with maternal ADHD. If there is a risk, it appears to be a small one.

The question then becomes how to balance that as yet uncertain risk against the disadvantage of discontinuing the effective psychostimulant medication. As the authors of this review conclude. It [ADHD] is associated with significant psychiatric comorbidities for women, including depression, anxiety, substance use disorders, driving safety impairment, and occupational impairment. The gold standard treatment includes behavioral therapy and stimulant medication, namely methylphenidate and amphetamine derivatives. Psychostimulant use during pregnancy continues to increase and has been associated with a small increased relative risk of a range of obstetric concerns. However, the absolute increases in risks are small, and many of the best studies to date are confounded by other medication use and medical comorbidities.

Thus, women with moderate-to-severe ADHD should not necessarily be counseled to suspend their ADHD treatment based on these findings. They advise that when functional impairment from ADHD is moderate to severe, the benefits of stimulant medications may outweigh the small known and unknown risks of medication exposure, and that "If a decision is made to take ADHD medication, women should be informed of the known risks and benefits of the medication use in pregnancy, and take the lowest therapeutic dose possible."

A newly-published systematic review by a British team identified48 qualitative and quantitative studies that explored "ADHD in primary care, including beliefs, understanding, attitudes, and experiences." The studies described primary care experiences in the U.S., Canada, Europe, Australia, Singapore, Iran, Pakistan, Brazil, and South Africa.

More than three out of four studies identified deficits in education about ADHD. Of particular concern was the training of primary care providers (PCPs), most of whom received no specific training on ADHD. In most places, a quarter or less of PCPs received such training. Even when such training was provided, PCPs often rated it as inadequate and said they did not feel they could adequately evaluate children with ADHD.

There was even less training for adult ADHD. A 2009 survey of 194 PCPs in Pakistan found that ADHD was not included at all in medical training there and that most learned from colleagues. Half readily admitted to having no competence, and less than one in five were shown to have adequate knowledge about ADHD. In a 2009 survey of 229South African PCPs, only 7 percent reported adequate training in childhood ADHD, and a scant one percent in adult ADHD.

These problems were by no means limited to fewer developed countries. A 2001 U.K. survey of 150 general practitioners found that only 6percent of them had received formal ADHD training. In a 2002 study of 499Finnish PCPs, only half felt confident in their ability to diagnose ADHD. A2005 survey of 405 Canadian PCPs likewise found that only half reported skill and comfort in diagnosis. In a 2009 survey of 400 U.S. primary care physicians, only 13 percent said they had received adequate training. A 2017 study of Swiss PCPs found that only five of the 75 physicians in the sample expressed competence in diagnosis.

Eight studies explored knowledge of DSM (Diagnostic and Statistical Manual of Mental Disorders) criteria and clinical guidelines among PCPs. Only a quarter of PCPs were using DSM criteria, and only one in five were using published guidelines. In a 1999 survey of 401 pediatricians in the U.S.and Canada, only 38 percent reported using DSM criteria. A 2004 survey of 723U. S. PCPs found only 44 percent used DSM criteria. In a 2006 UK study of 40general practitioners, only 22 percent were aware of ADHD criteria. In the same year, a survey of 235 U.S. physicians found that only 22 percent were familiar with ADHD guidelines, and 70 percent used child behavior in the office to make a diagnosis. More encouragingly, a 2010 U.S. study reported that the use of APA (American Psychological Association) guidelines by PCPs had expanded markedly between1999 and 2005, from one in eight to one in two.

Given these facts, it is unsurprising that many PCPs expressed a lack of confidence in treating ADHD. In a 2003 survey of 143 South African general practitioners, two-thirds thought it was difficult to diagnose ADHD in college students. A 2012 U.S. study of 1,216 PCPs found that roughly a third lacked confidence in diagnosis and treatment. More than a third said they did not know how to manage adult ADHD. In a 2015 survey of 59 physicians and138 nurses in the U.S., half lacked confidence in their ability to recognize ADHD symptoms. This was especially pronounced among the nurses. A 2001 U.K.survey of 150 general practitioners found that nine out of ten wanted further training on drug treatment, and more than one out of ten were unwilling to prescribe due to insufficient knowledge.

Misconceptions about ADHD were widespread. In a survey of380 U.S. PCPs, almost half thought ADHD medications were addictive, one in five thought ADHD was "caused by poor diet," more than one in seven thought "the child does it on purpose," and one in ten thought medications can cure ADHD. Some studies reported that many PCPs believed ADHD was related to the consumption of sugary food and drink. Others reported a gender bias. A 2002 U.S. study of395 PCPs found that when presented with boys and girls with parent-reported problems, they were significantly more likely to diagnose ADHD in boys.

A 2010 Iranian study of 665 PCPs found that 82 percent believed children adopted ADHD behavior patterns as a strategy to avoid obeying rules and doing assignments. One-third believed sugary food and drink contributed to ADHD. Only 6 percent believed it could be a lifelong condition. Half blamed dysfunctional families. The aforementioned large 2012 U.S. study similarly found that almost half of PCPs believed ADHD was caused by absent or bad parenting. More than half of 399 Australian PCPs surveyed in 2002 believed inadequate parenting played a key role. In a 2003 study of 48 general practitioners in Singapore, a quarter blamed sugar for ADHD. A 2014 survey of 57French pediatricians found that a quarter thought ADHD was a foreign construct imported into France, and 15 percent attributed it to bad parenting. In all, ten studies reported a widespread belief that ADHD was due to bad parenting, with ratios varying from over one in seven PCPs to more than half. They were particularly likely to attribute hyperactivity to dysfunctional families and to dismiss parents' views of hyperactivity as a medical problem as a way to deflect attention from inadequate parenting. While a third of the studies reported on stigma, the surprise was that it did not seem to play as big a role as expected. A 2012study in the Netherlands found that 74 physicians and 154 non-medical professionals matched by age, sex, and education showed no differences in the level of stigmatization toward ADHD.

On the other hand, the studies identified significant resource constraints limiting more effective understanding, diagnosis, and treatment. Given the complex nature of ADHD, the time required to gain relevant information, especially in the context of competing demands on the attention of PCPs, was a limiting factor. Many studies identified a need for better assessment tools, especially for adults.

Another major constraint was PCP's uneasiness about medication. Studies found a widespread lack of knowledge about treatment options, and more specifically the pros and cons of medication relative to other options. This often led to an unwillingness to prescribe.

Yet another limitation was the difficulties PCPs had in communicating with mental health specialists. One study found that less than one in six PCPs received communications from psychiatrists. Much of this was ascribed to "system failure": discontinuity of care, no central accountability, limited resources, buck-passing. Many PCPs were unsure who to turn to. Another problem is often faulty interactions between schools, parents, children, and providers. Parents often fail to keep appointments. Schools and parents often are less than cooperative in providing information. In a 2004 survey of 786 U.S. school nurses, less than half reported good levels of communication between schools and physicians. Schools and parents often apply pressure on PCPs to issue a diagnosis. In the U.S. survey of 723 PCPs, more than half reported strong pressure from teachers to diagnose ADHD, and more than two-thirds said they were under pressure to prescribe medication.

The authors noted, "The need for education was the most highly endorsed factor overall, with PCPs reporting a general lack of education on ADHD. This need for education was observed on a worldwide scale; this factor was discussed in over 75% of our studies, in 12 different countries, suggesting that lack of education and inadequate education was the main barrier to the understanding of ADHD in primary care.

"In addition, "time and financial constraints affect the opportunities for PCPs to seek extra training and education but also affect the communication with other professionals such as secondary care workers, teachers, and parents." The authors cautioned that only eleven of the 48 studies were published since 2010. Also, because it was a systematic review and not a meta-analysis, there was no way to evaluate publication bias.

They concluded, "Better training of PCPs on ADHD is, therefore, necessary but to facilitate this, dedicated time and resources towards education needs to be put in place by the service providers and local authorities."