The study had several limitations that prevent firmer conclusions about the drugs’ safety. The researchers couldn’t confirm that the participants actually consumed the prescriptions they filled, for instance, and they followed the participants for an average of just 16 months.
“That’s not a very long time for looking at cardiovascular risk, because cardiovascular risk extends over many years,” says Robert Myerburg, MD, a professor of medicine and physiology at the University of Miami Miller School of Medicine.
And despite being very large, the study may not have been big enough to detect small increases in risk, since heart attacks and other serious cardiovascular problems are relatively rare, says Philip Shaw, MD, an ADHD researcher at the National Institute of Mental Health who wrote an editorial accompanying the study. Indeed, only 2,228 of the study participants—one-half of 1%—experienced a heart attack, stroke, or sudden cardiac death.
More than 1.5 million adults in the United States take stimulants, according to the study. Most take the drugs for ADHD, although doctors sometimes prescribe stimulants off-label for depression-related fatigue, narcolepsy, and other conditions.
Although children with ADHD have received the lion’s share of attention from researchers and public-health officials, adults accounted for one-third of all prescriptions for ADHD medications in 2005. A previous study by the same group of researchers found no link between ADHD drugs and serious cardiovascular events in children and young adults, Shaw notes in his editorial.
People who take ADHD medications should continue to be aware of less serious side effects, such as insomnia and loss of appetite, Shaw says. But, he says, the study is “very reassuring” regarding cardiovascular risk.