Mike: Hello, I'm Mike Clarke, podcast editor for the Cochrane Library. The Cochrane Developmental, Psychosocial and Learning Problems Group produced several reviews relevant to the treatment of attention deficit hyperactivity disorder and the update for one of these, investigating the drug methylphenidate, was published in March 2023. Here's one of the authors, Maja Storm from the Psychiatric Research Unit, Region Zealand in Denmark, to tell us about the latest evidence.

Maja: Attention deficit hyperactivity disorder, or ADHD, is one of the most commonly diagnosed psychiatric disorders in childhood, with a prevalence between 3-5%. It's a heterogeneous disorder with symptoms of inattention, hyperactivity and impulsivity.
Methylphenidate has been used in its treatment since the late 1960s and remains the most commonly prescribed pharmacological treatment for ADHD. However, our review shows that much uncertainty still remains in regard to its effects and safety, because of the poor quality of the available evidence.
For the review, we investigated the benefits and harms of methylphenidate treatment for children and adolescents with ADHD in randomized trials. We now include 212 trials with a total of more than 16,000 participants. Their mean age was 9.8 years and the mean length of treatment across all the included trials was about one month.
Our primary outcomes were ADHD symptoms and serious adverse events. We also looked at general behaviour, non-serious adverse events and quality of life.
Pooling the results of the studies in meta-analyses suggest that methylphenidate may improve ADHD symptoms and general behaviour but causes many non-serious adverse events. There may be no effect on serious adverse events and quality of life, but very few trials provided data on these outcomes.
The high frequency of the non-serious adverse events and the fact that these are characteristic of methylphenidate makes it difficult to properly blind the participants, their caretakers and the trial outcome assessors to the allocated treatment. As such, study designs are needed that would avert unblinding during the trial, because unblinding causes a risk of systematic error, which affects the currently available trials.
Several other factors also limit our confidence in the results. Apart from the blinding challenges of methylphenidate trials, we judged that only 21 trials were at low risk of bias and 41% of the 212 included trials were fully or partially funded by the pharmaceutical industry. There was also a great deal of variation in all aspects of trial design and the short length of treatment makes it difficult to determine the long-term effects of methylphenidate, even though it is used for prolonged periods in the clinical setting.
In summary therefore, eight years after the publication of the first version of this review, the evidence remains too weak to provide a proper guide for practice. There is an urgent need for long-term, high-quality and large randomized trials that confront the challenges of blinding and treatment duration if patients and their carers are to have a reliable evidence base for the use of methylphenidate for ADHD.

Mike: If you would like to find out more about the more than 200 trials in this version of the review and watch for future updates if those much-needed new studies get done, it's available online. Just go to Cochrane Library dot com and search 'ADHD and methylphenidate' to find it.