More than one in five adult Americans took at least one medication commonly used to treat a psychiatric or behavioural disorder last year, and for women the figure was one in four, says new research.

Antidepressants are by far the most commonly-used mental health treatment, with over 20% of US women using them, says the study, from Medco Health Solutions, a pharmacy benefit manager (PBM). Anxiety treatments are also widely used by women and at almost twice the rate of men - the greatest use is among women aged 45-65, 11% of whom were on an anti-anxiety drug last year.

Many more boys than girls are prescribed treatments for attention deficit hyperactivity disorder (ADHD), but once they grow up that picture changes dramatically, says the report. Overall, the number of women on ADHD drugs was 2.5 times higher last year than in 2001, overtaking men in their use of these drugs. The most striking rise was seen in 22-44-year-old women, whose numbers rose 264% in 10 years.

"Over the past decade, there has been a significant uptick in the use of medicines to treat a variety of mental health problems; what is not as clear is if more people, especially women, are actually developing psychological disorders that require treatment or if they are more willing to seek out help and clinicians are better at diagnosing these conditions than they once were," commented Dr David Muzina, a psychiatrist and national practice leader of the Medco Neuroscience Therapeutic Resource Center.

The report also finds that while women are the predominant users of atypical antipsychotics, there has been a huge upswing in utilisation of these drugs among males as well, quadrupling in men aged 20-64 since 2001.

The overall results, that substantially more individuals are on psychotropic medications, is sobering and important, and understanding the reasons for this increase is the next critical goal, said Martha Sajatovic, professor of psychiatry at Case Western Reserve University School of Medicine. "The health care implications could be substantial, given increasing financial constraints on individuals and health care funding entities," she added.

The number of children (aged 19 and younger) on mental health drug treatments has risen over the past 10 years in all areas apart from antidepressants, which dropped substantially since the Food and Drug Administration (FDA) issued warnings on risks of suicidal ideation linked to these drugs in children. Use of ADHD drugs has also been on the decline in both boys and girls since 2005, and while boys are the primary users of ADHAD drugs and atypical antipsychotics, a greater number of girls take antidepressants and anti-anxiety drugs, says Medco.

It also finds that while the actual prevalence of children on atypical antipsychotics is low, at under 1%, the number doubled from 2001 to 2010.

"The fact that more children are being treated with atypicals is concerning, given that substantial weight gain is associated with the use of these drugs in this population, putting children at risk for diabetes and heart disease-related conditions," said Dr Mazina. "When using these drugs, children need to be monitored on a frequent basis to prevent against these serious health risks," he warned.