But a commentary published in the journal Clinical Pharmacology & Therapeutics(December 2008 issue) argues that adolescents remain overlooked by clinical researchers.

The authors - Bill Kapogiannis and Donald Mattison – point out that data collated by the US National Institute for Allergy and Infectious Disease (NIAID) found that only 5.4 per cent of 9,500 participants in HIV trials conducted at the institute were adolescents, while other research indicates similarly low levels in cancer studies.

They suggest that low participation rates in trials may be one reason why adolescents experience poor survival rates in cancer trials compared to children and adult patients

Kapogiannis and Mattison believe that it is critical that adolescents are actively recruited into clinical trials in order to avoid the risk of unpredictable pharmacological responses to medicines.

Physical changes, such as puberty, can change adolescent patients’ response to medicines, they note. And “in addition to physical changes, adolescents are susceptible to psychosocial factors that can affect taking the drug as directed, and place them at risk for additional disorders,” according to Kapogiannis and Mattison.

Adherence to medication regimens is a well-recognised problem with adolescents. Peer pressure, a wish to be more independent, and the use of illicit drugs or alcohol and mood disorders are all factors that are seen with adolescents and can impair compliance.

“Adolescents are exposed to many marketing campaigns and are at risk for misuse of products, but few studies look at this group,” write the authors. For example, studies suggest a third of adolescents use over-the-counter medicines at higher than the recommended label dose

Kapogiannis and Mattison also point out that the high rate of clinical trials in children masks the fact that in many cases they involve drugs predominantly marketed and used in adults.

Increasing the recruitment of adolescents into trials requires a wide-ranging approach that solves challenges relating to “trial design, safety, legal, ethical, regulatory, and operational factors,” according to the authors.

“Ethical research with adolescents should focus on two goals: protection from research risk and appropriate inclusion in clinical research that will improve our understanding of therapeutics,” they conclude.