The Food and Drug Administration (FDA) released a report Tuesday warning that ADHD drugs may be linked to long-lasting erections, a disorder known as priapism. According to the report, the FDA updated the drug labels on methylphenidate products to contain information about the “rare but serious risk” of priapism.

“Patients who take methylphenidate and develop erections lasting longer than four hours should seek immediate medical treatment to prevent long-term problems with the penis,” the FDA wrote. “If not treated right away, priapism can lead to permanent damage to the penis.” The FDA found that methylphenidate-induced priapism was likely to occur in males aged 8 to 33, but the median age of patients taking ADHD medications who had experienced priapism was about 12.5.

Priapism occurs when blood becomes contained and trapped in the penis, which can cause a painful and long-lasting erection. The Cleveland Clinic describes it as “a persistent, usually painful, erection that lasts for more than four hours and occurs without sexual stimulation.” There are two different types of priapism — low-flow and high-flow. Low-flow occurs when blood is trapped in the erection chambers, and can affect healthy men as well as those suffering from sickle-cell disease, leukemia, or malaria. High-flow is rarer, not usually painful, and can occur due to a ruptured artery.

Other drugs have been identified as potential triggers of priapism, including Desyrel, which is used to treat depression, or Thorazine, another mental illness drug. The FDA also notes that the non-stimulant drug Strattera, or atomoxetine, is another medicine used to treat ADHD that may also cause priapism. In fact, according to the FDA report, atomoxetine appears to be “more common in patients taking atomoxetine than in patients taking methylphenidate products.” The FDA urged health care professionals to be “cautious” when switching patients to atomoxetine.

The FDA review found that several patients required significant medical attention after experiencing priapism. Two required surgery, another needed shunt placement, and yet another required needle aspiration of the corpus cavernosum. Priapism is usually treated by ice packs that help reduce swelling or surgery. In surgical ligation, doctors tie off the artery that had been ruptured; sometimes they can perform aspiration, in which a needle drains blood to reduce the pressure.