A nationwide study from Finland provides evidence that adults diagnosed with attention-deficit hyperactivity disorder (ADHD) often reduce their use of antidepressants after beginning treatment for ADHD. The findings, published in Acta Psychiatrica Scandinavica, suggest that properly identifying and addressing ADHD may lessen the need for other psychiatric medications—particularly in adults who had previously been treated for symptoms like depression or anxiety.
ADHD is a neurodevelopmental condition marked by symptoms such as inattention, hyperactivity, and impulsivity. Although it’s often associated with children, it frequently persists into adulthood and may go unrecognized, especially when its symptoms overlap with mood disorders. Many adults with ADHD report long-standing difficulties in focus, task completion, or emotional regulation—challenges that may be misinterpreted as depression or anxiety.
Treatment for ADHD typically includes medication, such as stimulants like methylphenidate or amphetamines, and sometimes non-stimulant options like atomoxetine or guanfacine. These medications target core ADHD symptoms and can improve functioning across work, school, and relationships.
The research team noted that ADHD is often diagnosed after years of treatment for other psychiatric or physical symptoms. Because ADHD frequently co-occurs with depression and anxiety, it can be misdiagnosed or missed entirely. As a result, patients may receive antidepressants or anti-anxiety medications before the underlying ADHD is identified. The study aimed to investigate how treatment for ADHD affects the use of other medications—both psychiatric and non-psychiatric—and whether ADHD treatment leads to shifts in those patterns.
“There is active public discussion ongoing about the increase in ADHD diagnoses and the use of ADHD medication, especially in Finland. Here, on the other hand, we have excellent opportunities to conduct nationwide registry studies, so together with the study sponsor, Takeda, we decided to investigate this phenomenon. This is a large, comprehensive research project, and the first sub-study has already been published prior to the present article,” said study author Tuire Prami, a senior scientist at Oriola.
“We wanted to further examine, in a population representing the entire country, how ADHD patients had been treated before being diagnosed with ADHD and what medications they used after the diagnosis. These findings were compared with those from control subjects.”
The study drew on several nationwide Finnish registers to identify people newly diagnosed with ADHD between 2015 and 2020. Researchers used prescription data, diagnostic codes, and special reimbursement records to confirm ADHD status. The study included both children and adults, but special attention was paid to adult cases due to their higher levels of comorbid psychiatric medication use.
For each ADHD patient, the researchers matched up to four control individuals without any ADHD diagnosis or treatment. These controls were selected to match the ADHD patients by age, sex, and region.
Medication data spanned from 2010 through the end of 2021. The team used this information to track purchases of both ADHD-specific drugs and other medications, such as antidepressants, antipsychotics, antibiotics, and anti-inflammatory drugs. They examined changes in purchasing patterns before and after the ADHD diagnosis and compared these changes between ADHD patients and their matched controls.
The study also measured adherence (whether patients filled their prescriptions) and persistence (how long they stayed on medication) for ADHD drugs. This helped the researchers understand not just whether people were prescribed ADHD medication, but whether they actually used it over time.
The researchers found that many adults with ADHD had been using antidepressants prior to being diagnosed. In these individuals, antidepressant use dropped significantly after they began ADHD treatment. This trend was not mirrored in the control group, who did not receive ADHD diagnoses, suggesting the decline was tied to the new ADHD-focused care.
The drop in antidepressant use may reflect that treating ADHD directly can reduce symptoms that were previously being managed with other psychiatric medications. In other words, some adults may have been treated for depression or anxiety when the root issue was undiagnosed ADHD. Once they began ADHD medication, their need for antidepressants may have diminished.
In children, the researchers observed a similar pattern with non-psychiatric medications. Prior to their ADHD diagnosis, children with ADHD were more likely than their peers to be prescribed antibiotics, anti-inflammatory drugs, and asthma medications. After starting ADHD treatment, the use of these medications declined more steeply in the ADHD group than among controls. The authors note that this finding might relate to ADHD’s known association with infections and allergies in early life, although the exact reasons remain uncertain.
“Children who were later diagnosed with ADHD used more antibiotics and anti-inflammatory drugs than controls, and after the initiation of ADHD treatment, their use of these drugs decreased more than in matched controls,” Prami told PsyPost. “This was surprising and cannot solely be explained by the age-related decrease in the need for antibiotics in children as the age-matched controls did not show similar decrease.”
High levels of medication adherence were observed across the ADHD group. About 95% of patients filled their ADHD prescription at some point, and 80% did so within 10 days. These figures indicate that once ADHD was diagnosed, most patients began treatment promptly.
However, persistence varied by age. The youngest children remained on ADHD medication the longest, while adolescents had the highest dropout rates. Among adolescents who started ADHD treatment, fewer than half were still on their medication a year later. Adults had somewhat better persistence than teens but still showed high rates of discontinuation.
Seasonal trends also appeared in the data. In school-aged children and teenagers, ADHD drug purchases dropped during the summer, likely reflecting planned medication breaks during school holidays.
Another finding involved the types of ADHD medications prescribed. Methylphenidate was the most common initial drug, with younger children more often receiving sustained-release versions and adolescents and adults more often receiving extended-release forms. Most patients remained on their first prescribed ADHD drug for several months, but some switched to different medications over time, such as lisdexamphetamine or atomoxetine. These changes likely reflect individual variation in medication response or side effects.
In terms of other medications, adults with ADHD were more likely to have been prescribed antiepileptics, antipsychotics, and sleep medications before their diagnosis. This pattern supports the idea that untreated ADHD may lead to a complex medication history as patients seek relief for related symptoms. Melatonin and acid reflux medications were also more common in ADHD patients, possibly reflecting the psychological and physical strain of living with undiagnosed ADHD.
“ADHD can be challenging to diagnose,” Prami said. “This is especially true in adults—where the diagnosis is already delayed—who may first receive treatment for symptoms or for another presumed condition, such as depression.”
“Once ADHD medication is prescribed, patients tend to be adherent in initiating the treatment. Among the youngest children, medication is continued for the longest duration. This result suggests that young patients to whom the medication has been prescribed have benefited from it, and the parents, as they are responsible for the administration, have been committed to the treatment. Adolescents aged 13–17, on the other hand, are the most likely to discontinue ADHD medication soon after starting it. Despite independent responsibilities in this age group, supporting both adolescent themselves and their families not only at initiation but during the medical treatment seems crucial.”
While the study does not prove that treating ADHD directly reduces the need for antidepressants, the observed pattern suggests that improved recognition and treatment of ADHD could streamline psychiatric care and reduce the need for multiple medications.
As with all registry-based studies, the researchers could only observe what was recorded in national databases. They did not have direct access to clinical interviews or symptom checklists, so the reasons behind changes in medication use remain speculative. The study also could not account for medications obtained without a prescription, such as over-the-counter melatonin or non-prescription antihistamines.
Still, the size and scope of the dataset allowed the researchers to spot population-level trends that may not be visible in smaller clinical studies. The findings raise questions about how often ADHD is misdiagnosed or underdiagnosed, particularly in adults.
“This is a very large-scale project for which we have collected extensive research data,” Prami said. “Next, we plan to publish results on comorbidities and causes of death among ADHD patients and controls. In addition to health information, data have also been collected on variables such as socioeconomic status, education, and criminality. Using these, our publication plan includes several more sub-studies. We are also open to hearing research ideas from outside our group.”
“Finland provides unique opportunities for conducting registry-based research, thanks to its comprehensive, high-quality nationwide health and population registries. Our research group’s diverse and solid expertise enables us to carry out large-scale projects using valuable databases.”
The study, “Use of Antidepressants Decreased After Initiation of ADHD Treatment in Adults—A Finnish Nationwide Register Study Describing Use of ADHD and Non-ADHD Medication in People With and Without ADHD,” was authored by Elisa Westman, Tuire Prami, Alvar Kallio, Ilona Iso-Mustajärvi, Joel Jukka, Paavo Raittinen, Maarit J. Korhonen, Anita Puustjärvi, and Sami Leppämäki.
