What is Sluggish Cognitive Tempo and is it Relevant to ADHD?

Attention-Deficit/Hyperactivity Disorder (ADHD) is one of the most common neurodevelopmental conditions, yet many young people, especially girls, receive a diagnosis late or not at all. This matters, because a delayed diagnosis often means missed opportunities for support, treatment, and improved long-term outcomes. A recent study by Barclay and colleagues (2024) sheds new light on why ADHD recognition is inconsistent, and what we can do about it.

The Study:

Researchers analyzed data from nearly 10,000 children in the UK Millennium Cohort Study. They compared children whose ADHD was recognized early (ages 5–7), later (ages 11–14), or not recognized at all, despite evidence of symptoms. The team also looked at differences between boys and girls to better understand why diagnosis patterns vary by sex.

Key Findings:

1. Severity Drives Earlier Recognition
   Children who were diagnosed at a younger age often had more visible difficulties: emotional outbursts, peer conflict, conduct issues, and lower cognitive scores. In other words, the “louder” and more disruptive the symptoms, the more likely ADHD was flagged early.
   
   
2. “Quieter” ADHD May Be Overlooked
   Children with stronger prosocial skills or higher cognitive ability were less likely to be recognized, even if they had clear ADHD symptoms. These children may be able to “mask” their difficulties, or adults may misinterpret their struggles as personality quirks rather than signs of ADHD.
   
   
3. Emotional Dysregulation Matters
   Emotional dysregulation—big swings in mood, difficulty calming down, intense frustration—was strongly linked to recognized ADHD in boys, but not in girls. This suggests that clinicians may pay closer attention to these behaviors in boys, while overlooking them in girls.
   
   
4. Co-occurring Conditions Can Influence Diagnosis
   Children with autism were more likely to have their ADHD identified. On the flip side, those who engaged in more physical activity were slightly less likely to be recognized, though the reasons for this are not yet clear.
   
   

What This Means for Clinicians:

The study highlights the importance of looking beyond the “classic” hyperactive child stereotype when considering ADHD. Clinicians should:

• Pay attention to symptoms of emotional dysregulation, even if they are not part of standard diagnostic checklists.
  
  
• Consider ADHD in children with good grades or strong social skills if other symptoms are present.
  
  
• Be mindful of gender differences, since girls may be more likely to internalize symptoms or present with inattentiveness rather than hyperactivity.
  
  

What This Means for Parents and Patients:

If you’re a parent, it’s important to trust your observations. If your child struggles with focus, organization, or emotional regulation—even if they are doing well academically or socially—these could still be signs of ADHD. Advocating for an evaluation can make a big difference.

Moving Forward

This study makes clear that ADHD is not one-size-fits-all. Recognition often depends on how symptoms show up, how disruptive they appear, and even the child’s gender. By broadening our awareness and refining our screening practices, we can ensure that fewer children slip through the cracks and more receive the support they need early in life.

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Parents and teachers often ask: Does ADHD medication actually improve grades and school performance? The answer is: yes, but with important limitations. Medications are very effective at reducing inattention, hyperactivity, and impulsivity but their impact on long-term academic outcomes like grades and test scores is not as consistent.

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In the Classroom

The medications for ADHD consistently: Improve attention, reduce classroom disruptions, increase time spent on-task and help children complete more schoolwork and homework. Medication can help children with ADHD access learning by improving the conditions for paying attention and persisting with work.

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Does Medication Improve Test Scores and Grades?

This is where the picture gets more complicated.  Medications have  stronger effect on how much work is completed but a weaker effect on accuracy. Many studies show that children on medication attempt more problems in reading, math, and spelling, but the number of correct answers doesn’t always improve as much. Some studies find small but significant improvements in national exam scores and higher education entrance tests during periods when children with ADHD are medicated.

Grades improve, as well, but modestly. Large registry studies in Sweden show that students who consistently take medication earn higher grades than those who don’t. However, these gains usually do not close the achievement gap with peers who do not have ADHD.

Keep in mind that small improvements for a group as a whole mean that some children are benefiting greatly from medication and others not at all.  We have no way of predicting which children will improve and which do not. 

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Medication Alone Isn’t Enough

Academic success depends on more than just reducing inattention, hyperactivity and impulsivity. Skills like organization, planning, studying, and managing long-term projects are also critical.  Medication cannot teach these skills.

So, in addition to medication, the patient's treatment program should include educational support (tutoring, structured study skills programs), behavioral interventions (parent training, classroom management strategies), and accommodations at school (extra time, reduced distractions, organizational aids) Parents should discuss with their prescriber which of these methods would be appropriate.

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Conclusions 

ADHD medication is a powerful tool for reducing symptoms and supporting learning. It improves test scores and grades for some children, especially when taken consistently. But it is not a magic bullet for academic success. The best results come when medication is combined with educational and behavioral supports that help children build the skills they need to thrive in school and beyond.

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ADHD is usually framed as a dopamine-and-norepinephrine condition, but recent studies have revealed that serotonin may also play a significant role. To delve deeper into this, we conducted a systematic literature review of studies looking at serotonin, its receptors, and the serotonin transporter (SERT) in relation to ADHD. The result: serotonin appears to be an important piece of the puzzle, but the overall picture is quite complex.

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‍An ADHD & Serotonin Literature Review:

‍The authors searched the literature without time limits and screened thousands of records to end up with 95 relevant publications. Those included animal/basic-science work, neuroimaging, pharmacodynamics, a couple of large genetic/transcriptomic studies (GWAS and a cortico-striatal TWAS), and a few clinical reports. Each paper was graded for quality: 17 high, 59 medium, and 19 low.

The Results:

• Most studies support a serotonergic role. About 81% (77/95) of the papers reported altered serotonin production, binding, transport, or degradation linked to ADHD or ADHD-like behaviors.
  
  
• Multiple lines of evidence: animal models frequently show that changing serotonin levels or receptor activity alters hyperactivity and impulsivity; human imaging and clinical studies provide supportive but smaller and sometimes mixed signals; genetic/transcriptomic work points to serotonin-related pathways among many implicated systems.
  
  
• Receptors and SERT matter: Multiple serotonin receptor subtypes (5-HT1A, 1B, 2A, 2C, 7) and SERT show associations with impulsivity, hyperactivity, attention, or brain activity patterns in ADHD models and some human studies.
  
  
• Mixed and conflicting data: Central measures (brain, CSF) more often show serotonin deficits, while peripheral measures (platelets, plasma) sometimes show higher serotonin — methodological differences likely explain some contradictions.
  
  
• Drugs used for ADHD can affect serotonin: Stimulants and non-stimulant drugs approved by FDA for treating ADHD (e.g., methylphenidate, atomoxetine, extended release viloxazine) or under investigation (centafafadine) have direct or indirect effects on serotonin systems, supporting the idea that monoamines interact rather than acting separately.  Because drugs that mainly affect serotonin are not useful for ADHD it seems likely that a pathway forward for ADHD drug development would be drugs that target multiple neurotransmitter systems.  A complex treatment for an etiologically complex disorder.
  
  

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The Role of Serotonin in ADHD: What's The Take-Away?

As the study points out, the idea that serotonin may play a role in the neurobiology of ADHD is not new, but this literature review “identified multiple individual strands of evidence gathered over several decades and brought them into a more coherent focus”. It concludes that serotonergic neurotransmission is implicated in ADHD.  This doesn’t mean variations in serotonin levels cause ADHD, but that serotonin may be a plausible target for future treatments and research.

ADHD is polygenic and multi-systemic. For now, clinicians and patients should view serotonin as part of a complex network that may contribute to ADHD symptoms.  More research is needed before making treatment decisions based on these findings. 

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