Why lighting up might lead to a hard-on that doesn't go down.

More states may be legalizing marijuana, but that doesn’t mean weed is harmless. In fact, for the men out there, it may come with an unexpected side effect: unwanted, lengthy erections. The kind of erections that would send a guy to the emergency room because there’s just something really wrong.

And yes, this has happened. In a new case report published in the Journal of Cannabis Research, scientists detail the story of a 32-year-old man from Georgia who went to the ER, once for a 12-hour erection and two weeks later for a six-hour erection. Upon examination, his penis was erect, swollen, and tender. He told doctors that he smoked marijuana “several nights per week for the past six months.” He also said he smoked weed two hours before each long-lasting erection.

There’s a medical term for these hard-ons that last this long and it’s priapism. Officially, priapism describes an erection that goes on for more than four hours and is unrelated to sexual activity. Priapism can be dangerous, and this guy was smart to seek medical care. When blood is trapped in the penis for more than 12 hours, the tissues get deprived of oxygen and can become damaged, affecting future erections.

The man told doctors that he didn’t have any illnesses that would increase his risk for priapism, including sickle cell disease. (This condition affects the hemoglobin molecules in red blood cells, which ferry oxygen throughout the body.) He also didn’t take any meds, like those for blood pressure or psychiatric illnesses, which could lead to super long erections, either. Basically, there wasn’t any other reason for his priapism aside from his weed habit, which happened to coincide.

However, he did say that these long-lasting erections weren’t new for him. When he was a teenager he used weed habitually and often got four-hour erections. (He didn’t go to the ER for those; one assumes they subsided on their own.) In his 20s, he stopped using, and the strange erections stopped. Six months ago, when he started smoking weed again, the erections came back. He said he had “at least a dozen” of them in the past six months, but all went away within four hours, so he didn’t need to be treated.

The authors of the study call this the first case of priapism associated with marijuana use, and there are several reasons why weed could play a role. First, psychoactive compounds in marijuana that interact with cannabinoid receptors may affect a nerve pathway that allows the body to lose an erection. Cannabinoids may also directly affect blood vessels or lead to a blood clot.

The man was successfully treated when doctors inserted a fine needle into his penis and gave him a decongestant drug called phenylephrine. And by that we mean he went back to flaccid—or as the report calls it “detumescence.” Doctors sent him home with a referral to internal medicine and urology providers, but the researchers note that they don’t know what happened with his case after that.

Let’s hope docs are at least on alert: The study ends with the authors noting that since marijuana is so popular, priapism may rear its head (sorry, penis puns!) again in ERs near you.

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