Adults are now the prime market for ADHD drugs in U.S.

Shire CEO Flemming Ornskov

Drugmakers often do pediatric studies of their drugs to broaden the markets. But in the case of drugs for attention deficit and hyperactivity disorder (ADHD) that were primarily developed with children in mind, the market is developing the other way, with more adults now taking the drugs than children.

In fact, growth in use of ADHD drugs by adults in the U.S is growing at nearly twice the rate of the overall market, Shire ($SHPG) CEO Flemming Ornskov told analysts in a call recently, Bloomberg reports. The company, whose Vyvanse is the leading ADHD treatment and approved for both children 6 to 17 and adults, says 53% of prescriptions for ADHD drugs in 2014 were for adults, up from 39% in 2007, and amounting to 63 million prescriptions last last year.

Shire has taken advantage of that information to boost Vyvanse sales. "We've shifted more effort into the adult ADHD market, which is now more than half of the overall market and has the highest growth," Ornskov told analysts. The company is directing sales reps to spend more time telling doctors about studies on adult use of ADHD drugs.

And it has paid off. Vyvanse, Shire's best-selling product, churned out $1.4 billion in sales last year, up 18% on 4% prescription growth. That was more than double sales of closest branded rival. Concerta from Johnson & Johnson (J&J) had $599 million in sales, although it faces generic competition, as does Novartis' ($NVS) Ritalin. In Q1, Vyvanse raked in $417 million in sales, up 17%, but that was helped by another market area for the drug, binge eating disorder, for which the FDA approved it in January. The company is also studying the drug for treating ADHD in preschoolers as it looks to continue the expansion of markets for the drug.

Studies show the reasons for the migration of ADHD drug use to adults are several, Bloomberg reports. Children with ADHD don't necessarily outgrow the condition when they become adults and findings that the condition can be inherited has led to parents of children with ADHD to sometimes get diagnosed with the condition.

Shire, which is based in Ireland, says in Europe ADHD drugs are still primarily taken by children, with 74% of the prescriptions written for them. But some markets there are also starting to shift, like in Scandinavia. "Sweden is one of our fastest uptick markets, even beating the benchmarks for the U.S.," Ornskov told analysts.

- here's the Bloomberg story

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