Research shows that ADHD stimulant medications such as Ritalin and Adderall appear linked to a heightened risk for cardiomyopathy (weakening of the heart muscle) — and the risk grows with time.

Overall, people ages 20 to 40 who were on a medication for attention-deficit/hyperactivity disorder (ADHD) were 17 percent more likely to have cardiomyopathy at one year and 57 percent more likely to have cardiomyopathy at eight years compared to peers who weren’t taking the drugs.

“The longer you leave patients on these medications, the more likely they are to develop cardiomyopathy, but the risk is still very low,” said study lead author Pauline Gerard.

The study was based on data from 80 hospitals across the United States, looking at people ages 20 to 40. Gerard’s team compared rates of cardiomyopathy among patients with ADHD who took stimulant meds and people who were matched by age, sex, and health conditions but did not take the drugs.

The study showed that over a period of 10 years, the relative risk for cardiomyopathy rose among people taking stimulant meds for about eight years, then tapered off during the last two years.

However, in absolute numbers, the incidence of cardiomyopathy was still quite low. At the 10-year mark, just under 1 percent of patients taking ADHD medications was found to have a weakened heart.