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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.
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.
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.
Faraone, S. V., Ward, C. L., Boucher, M., Elbekai, R., & Brunner, E. (2025). Role of serotonin in the neurobiology of attention-deficit/hyperactivity disorder: a systematic literature review. Expert Opinion on Therapeutic Targets, 1–18. https://doi.org/10.1080/14728222.2025.2552324
Although there has been much research documenting that ADHD adults are at risk for other psychiatric and substance use disorders, relatively little is known about whether ADHD puts adults at risk specifically for somatic medical disorders.
Given that people with ADHD tend toward being disorganized and inattentive, and that they tend to favor short-term over long-term rewards, it seems logical that they should be at higher risk for adverse medical outcomes. But what does the data say?
In a systematic review of the literature, Instances and colleagues have provided a thorough overview of this issue. Although they found 126 studies, most were small and were of "modest quality". Thus, their results must be considered to be suggestive, not definitive for most of the somatic conditions they studied.
Also, they excluded articles about traumatic injuries because the association between ADHD and such injuries is well established. Using qualitative review methods, they classified associations as being a) well-established; b) tentative, or c) lacking sufficient data.
Only three conditions met their criteria for being a well-established association: asthma, sleep disorders, and obesity.
They found tentative evidence implicating ADHD as a risk factor for three conditions: migraine headaches, celiac disease, and diseases of the circulatory system.
These data are intriguing, but cannot tell us why ADHD people are at increased risk for somatic conditions. One possibility is that suffering from ADHD symptoms can lead to an unhealthy lifestyle, which leads to increased medical risk. Another possibility is that the biological systems that are dysregulated in ADHD are also dysregulated in some medical disorders. For example, we know that there is some overlap between the genes that increase the risk for ADHD and those that increase the risk for obesity. We also know that the dopamine system has been implicated in both disorders.
Instances and colleagues also point out that some medical conditions might lead to symptoms that mimic ADHD. They give sleep-disordered breathing as an example of a condition that can lead to the symptom of inattention.
But this seems to be the exception, not the rule. Other medical conditions co-occurring with ADHD seem to be true comorbidities, rather than the case of one disorder causing the other. Thus, primary care clinicians should be alert to the fact that many of their patients with obesity, asthma, or sleep disorders might also have ADHD.
By screening such patients for ADHD and treating that disorder, you may improve their medical outcomes indirectly via increased compliance with your treatment regime and an improvement in health behaviors. We don't yet have data to confirm these latter ideas, as the relevant studies have not yet been done.
Serotonin is a key chemical in the body that helps regulate mood, behavior, and also many physical functions such as sleep and digestion. It has also been linked to how ADHD (attention-deficit/hyperactivity disorder) develops in the brain. This study looks at how serotonin may be involved in both the mental health and physical health conditions that often occur alongside ADHD.
It is well-established that ADHD is more than just trouble focusing or staying still. For many, it brings along a host of other physical and mental health challenges. It is very common for those with ADHD to also have other diagnosed disorders. For example, those with ADHD are often also diagnosed with depression, anxiety, or sleep disorders. When these issues overlap, they are called comorbidities.
A new comprehensive review, led by Dr. Stephen V. Faraone and colleagues, delves into how serotonin (5-HT), a major brain chemical, may be at the heart of many of these common comorbidities.
Serotonin is a neurotransmitter most often linked to mood, but its role in regulating the body has much broader implications. It regulates sleep, digestion, metabolism, hormonal balance, and even immune responses. Although ADHD has long been associated with dopamine and norepinephrine dysregulation, this review suggests that serotonin also plays a central role, especially when it comes to comorbid conditions.
This research suggests that serotonin dysregulation could explain the diverse and sometimes puzzling range of symptoms seen in ADHD patients. It supports a more integrative model of ADHD—one that goes beyond the brain’s attention, reward and executive control circuits and considers broader physiological and psychological health.
future research into the role of serotonin could help develop more tailored interventions, especially for patients who don't respond well to stimulant medications. Future studies may focus on serotonin’s role in early ADHD development and how it interacts with environmental and genetic factors.
This study is a strong reminder that ADHD is a complex, multifaceted condition. Differential diagnosis is crucial to properly diagnosing and treating ADHD. Clinicians' understanding of the underlying link between ADHD and its common comorbidities may help future ADHD patients receive the individualized care they need. By shedding light on serotonin’s wide-reaching influence, this study may provide a valuable roadmap for improving how we diagnose and treat those with complex comorbidities in the future.
Taiwan's National Health Insurance program is a single-payer system that covers 99.6% of the island's 23 million residents. It includes family relationships.
This enabled a Taiwanese study team to examine the comorbidity of psychiatric disorders among close relatives in the entire population over eleven years, beginning at the start of 2001 and concluding at the end of2011.
For greater certainty of diagnosis, only persons twice diagnosed with the same psychiatric disorder were included as index individuals. There were 431,887 index patients, 152,443 of whom were ADHD index patients.
These index patients were then compared with all of their first-degree relatives (FDRs): parents, children, siblings, and twins. This produced 1,017,430 patient-FDR pairs, of which 401,301 were ADHD patient-FDR pairs.
Next, four controls were matched by age, gender, and type relative to each case, resulting in 4,069,720 control pairs.
After adjusting for age, gender, urbanization, and income level, ADHD patients were seven times more likely than controls to have first-degree relatives with ADHD. They were also seven times more likely to have FDRs with major depressive disorder, four times more likely to have FDRs with autism spectrum disorder, twice as likely to have FDRs with bipolar disorder, and 80%more likely to have FDRs with schizophrenia.
For years, a persistent concern has shadowed the treatment of Attention-Deficit/Hyperactivity Disorder (ADHD): Does the medication eventually stop working? Patients often report that their symptoms seem to return despite consistent use, leading to "dose escalation" or "medication holidays." A new systematic review from Sam Cortese’s team published in CNS Drugs finally puts these concerns to the test by synthesizing decades of empirical research.
Before diving into the findings, you must understand two often-confused phenomena:
The review analyzed 17 studies covering over 10,000 individuals, and the results provide a much-needed reality check for the clinical community.
The researchers found preliminary evidence that acute tolerance (tachyphylaxis) can occur within a 24-hour window.
The most important finding is that tolerance does not commonly develop to the therapeutic effects of ADHD medication in the long term. In one landmark study following children for up to 10 years, only 2.7% of participants lost their response to methylphenidate without a clear external explanation. Doses, when adjusted for natural body growth, remained remarkably stable over years of treatment.
Consistent with the lack of therapeutic tolerance, the body does not become tolerant to the physical side effects of stimulants. Increases in heart rate and blood pressure typically persist for as long as the medication is taken. This underscores why clinicians must continue monitoring cardiovascular health throughout the entire duration of treatment.
If it’s Not Tolerance, What Is It?
If "tolerance" isn't real, why do some patients feel their medication is failing? The review suggests clinicians look at these alternative explanations:
Why This Matters
These results provide clinicians the confidence to tell patients that their medication is unlikely to "wear out" permanently. Rather than immediately increasing a dose when symptoms flare, the first step should be a "clinical deep dive" into the patient's lifestyle, stress levels, and adherence.
For researchers, the review highlights a major gap: most existing studies are small, dated, or of low quality. There is a dire need for robust, longitudinal studies that track both the brain's response and the patient's environment over several years.
For people with ADHD, while your body might get "used to" the initial "buzz" of a stimulant within hours, its ability to help you focus and manage your life remains remarkably durable over the years.
The Background:
Concerns remain about how ADHD and methylphenidate (MPH) use might affect children's health and growth, and especially how it may affect their adult height. While some studies suggest disrupted growth and a possible biological mechanism, the impact of ADHD prevalence and MPH use is still unclear. Children with ADHD may develop unhealthy habits – irregular eating, low physical activity, and poor sleep – that can contribute to obesity and reduced height. MPH’s appetite-suppressing effect can lead to skipped meals or overeating. Since growth hormone is mainly released during deep sleep, chronic sleep deprivation could plausibly slow growth and impair height development; however, a clear link between ADHD, MPH use, overweight, and shorter stature has never been firmly established.
The Study:
South Korea has a single payer health insurance system that covers more than 97% of its population. A Korean research team used the National Health Insurance Service database to perform a nationwide population study to explore this topic further.
The study involved 34,850 children, of whom 12,866 were diagnosed with ADHD. Of these children, 6,816 (53%) had received methylphenidate treatment, while 6,050 (47%) had not. Each patient with ADHD was precisely matched 1:1 by age, sex, and income level to a control participant without ADHD. The sex ratio was comparable in all groups.The team used Body Mass Index (BMI) as an indicator of overweight and obesity.
The Results:
The researchers found that being diagnosed with ADHD was associated with 50% greater odds of being overweight or obese as young adults, and over 70% greater odds of severe obesity (BMI > 30) compared to matched non-ADHD controls, regardless of whether or not they were medicated.
Those diagnosed with ADHD, but not on methylphenidate, had 40% greater odds of being overweight or obese, and over 55% greater odds of becoming severely obese, relative to matched non-ADHD controls.
Methylphenidate users had 60% greater odds of being overweight or obese, and over 85% greater odds of becoming severely obese, relative to matched non-ADHD controls.
There were signs of a dose-response effect. Less than a year’s exposure to methylphenidate was associated with roughly 75% greater odds of becoming severely obese, whereas exposure over a year or more raised the odds 2.3-fold, relative to matched non-ADHD controls. Using MPH increased the prevalence of overweight from 43.2% to 46.5%, with a greater prevalence among those using MPH for more than one year (50.5%).
It is important to note that most of this effect was from ADHD itself, with methylphenidate only assuming a predominant role in severe obesity among those with longer-term exposure to the medicine.
As for height, children with ADHD were no more likely to be short of stature than matched non-ADHD controls. Being prescribed methylphenidate was associated with slightly greater odds (7%) of being short of stature, but there was no dose-response relationship.
Conclusion:
The team concluded, “patients with ADHD, particularly those treated with MPH, had a higher BMI and shorter height at adulthood than individuals without ADHD. Although the observed height difference was clinically small in both sexes and age groups, the findings suggest that long-term MPH exposure may be associated with growth and body composition, highlighting the need for regular monitoring of growth.” They also point out that “Despite these findings, the clinical relevance should be interpreted with caution. In our cohort, the mean difference in height was less than 1 cm (eg, maximum −0.6 cm in females) below commonly accepted thresholds for clinical significance.” Likewise, increases in overweight/BMI were small.
One problem with interpreting the BMI/obesity results is that some of the genetic variants that cause ADHD also cause obesity. If that genetic load increases with severity of ADHD than the results from this study are confounded because those with more severe ADHD are more likely to be treated than those with less severe ADHD.
Due to these small effects along with the many study limitations noted by the authors, these results should be considered alongside the well-established benefits of methylphenidate treatment.
What do we mean by expert? In simple terms, an expert possesses in-depth knowledge and specialized training in a particular field. In order to be considered an expert in any field, a person must have both deep knowledge of and competence in their specific area of expertise. Experts have a background that includes education, research, and experience. In the world of mental health and psychology, this typically means formal credentials (a PhD, MD, etc) in addition to years of study, peer-reviewed publications, and/or extensive clinical experience.
Experts are recognized by their peers (and often by the public) as reliable authorities on a specific topic. Experts usually don’t make big claims without evidence; instead, they cite studies and speak cautiously about what the evidence shows.
Tip: Those looking for likes and clicks will often speak in absolutes (e.g., “refined sugar makes your ADHD worse, but the Keto Diet will eliminate ADHD symptoms”) while experts will use language that emphasizes evidence (e.g., “research has proven that there is no ‘ADHD Diet’, but some evidence has suggested that certain individuals with ADHD may benefit from such dietary interventions as limiting food coloring or increasing omega fatty acids.”)
Social media has created an incredible opportunity for those with ADHD to gain access to invaluable resources, including the creation of communities by and for those with ADHD. Many people with ADHD report feeling empowered and less alone by connecting with others online. These online social platforms provide a space for those with ADHD to share their own perspectives and their lived experience with the disorder. Both inside and outside of mental health-related communities, social media is a powerful tool for sharing information, reducing stigma, and helping people find community. When someone posts about their own ADHD challenges or tips, it can reassure others that they’re not the only ones facing these issues. This kind of peer support is valuable and affirming.
It is vital for those consuming this media, however, to remember that user-generated content on social media is not vetted or regulated. Short TikTok or Instagram videos are designed to grab attention, not to teach nuance or cite scientific studies. As it turns out, most popular ADHD posts are misleading or overly simplistic, at best. One analysis of ADHD TikTok videos found that over half were found to be “misleading” by professionals. Because social feeds reinforces what we already believe (the “echo chamber” effect, or confirmation bias), we can easily see only content that seems to confirm our own experiences, beliefs, or fears.
Stories aren’t a substitute for expert guidance.
It’s important to recognize the difference between personal experience and general expertise. Having ADHD makes you an expert on your ADHD, but it does not make you an expert on ADHD for everyone. Personal stories are not scientific facts. Even if someone’s personal journey is true, the same advice or experience may not apply to others. For instance, a strategy that helps one person focus might have no effect– or possibly even a negative effect– on someone else.
Researchers have found that most ADHD content on social media is based on creators’ own experiences, not on systematic research. In one study, almost every TikTok ADHD creator who listed credentials actually just cited their personal story. Worse, about 95% of those videos never noted that their tips might not apply to everyone (journals.plos.org.) In other words, they sound absolute even though they really only reflect one person’s situation. It’s easy to misunderstand the condition if we take those singular experiences as universal facts.
So how can you tell when someone is speaking from expertise rather than personal experience or hearsay? Experienced professionals usually speak cautiously, rather than in absolutes. They tend to say things like “research suggests,” “some studies show,” or “evidence indicates,” rather than claiming something always or never happens. As one health-communication guide puts it, a sign of a trustworthy source is that they do not speak in absolutes; instead, they use qualifiers like “may,” “might,” or refer to specific studies. For example, an expert might say, “Some people with ADHD may have difficulty with organization,” instead of “ADHD people always lose things.”
Real experts also cite evidence. In science and psychology, experts usually share knowledge through peer-reviewed articles, textbooks, or professional conferences – not just social media posts. Reliable health information is typically backed by references to studies published in reputable journals.
If someone makes a claim online, ask: Do they point to research, or is it just their own testimony? This is why it’s wise to prefer content where the author is a recognized authority (like a doctor or researcher) and where references to scientific studies or official guidelines are provided. In fact, advice from sites ending in “.gov”, “.edu”, or “.org” (government, university, or professional organizations) tends to be more reliable than random blogs. When in doubt, look up who wrote the material and whether it cites peer-reviewed research.
When navigating mental health information online, remember these key points:
If you see sweeping statements like “This one habit will predict if you have ADHD” or “Eliminating this one food will cure your ADHD symptoms”--- that’s a red flag. Instead, the hallmark of expert advice is a tone of humility (“evidence suggests,” “it appears that,” etc.), clear references to studies or consensus statements, and an acknowledgment that individual differences exist.
At the same time, we need to acknowledge that community voices are incredibly valuable – they help us feel understood and less alone. The goal is not to dismiss personal stories, but to balance them with facts and evidence-based information. Let lived experience spark questions, but verify important advice with credible sources. Follow trusted organizations (for example, the National Institutes of Health, CDC, or ADHD specialist groups) and mental health professionals who communicate carefully. Use the online ADHD community for support and sharing tips, but remember it’s just one piece of the puzzle.
By being a savvy reader (checking credentials, looking for cited evidence, and spotting overgeneralizations), you can make the most of online ADHD content. In doing so, you give yourself both the empathy of community and the accuracy of real expertise. That way, you’ll be well-equipped to separate helpful insights from hype and to keep learning from both personal stories and science-based experts.
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