John* had an erection that hurt worse than anything he could recall in his life—and it just wouldn’t go away.

At first, the 55-year-old Florida resident figured his alprostadil, an injectable medication for erectile dysfunction (ED), was simply taking longer than usual to wear off.

So he popped some Tylenol to fight the pain while he waited for his erection to go away.

And he waited…and waited.

Seven hours later, the throbbing in his mid-shaft was only getting worse—and his erection still remained. Still, he figured the erection and the pain would eventually go away on their own.

But after 7 more hours, panicked by the severity of the pain—and the persistence of the erection—he headed to the emergency room.

There, doctors diagnosed him with priapism, the official term for a prolonged erection that lasts longer than 4 hours.

And while it may sound like a punch line, John’s 14-hour experience with priapism confirms that it’s no joke.

In fact, priapism can cause serious damage to your penis if it’s not treated properly.

Read on to find out what’s causing these endless erections, and what you can do if yours won’t quit.

How common is priapism?

Despite what watching commercials for Viagra or Cialis may have you think, priapism is not as common as it may seem, even in guys who take those drugs for ED.

In fact, over a 4-year period, only about 8,700 guys went to the emergency room for the condition nationwide, a study published in the Journal of Sexual Medicine found.

Even though these prolonged erections are rare, they can have serious consequences to your penis—and your sex life—if you let them go untreated.

Why do you get a prolonged erection?

An erection occurs when you’re aroused, and the blood vessels in your penis relax and open up so more blood can flow in.

The pressure of the increased blood flow constricts the deep dorsal vein at the bottom of your penis so the blood can’t flow out, making your penis hard and erect.

After you ejaculate, your blood vessels in your penis should go back to their normal size, and the extra blood will flow out, says Daniel Williams, IV, M.D., an associate professor of urology, obstetrics, and gynecology at the University of Wisconsin School of Medicine and Public Health.

Sometimes, though, your blood vessels will stay relaxed, even though you’re no longer aroused.

But since the dorsal vein is still constricted, the extra blood flow stays in your penis instead of flowing back out.

This gives you a prolonged erection, says Dr. Williams.

When that happens, all of that pent up blood will make you penis feel unusually hard, swollen, and painful.

How do ED drugs increase your risk of a prolonged erection?

While ED meds can increase your risk of priapism, the chances are still really, really low, Dr. Williams says. (It’s difficult for experts to give an actual number, since some men may be too embarrassed to seek treatment.)

In many cases in men with ED, their blood flow is compromised, so the blood flow into their penis is impeded, too. As a result, they have difficulty growing hard.

Oral drugs like Viagra and Cialis, or injectable meds like alprostadil, help the blood vessels in the penis relax and open, so you can get and maintain an erection, Dr. Williams says.

But in rare cases, the meds cause the blood vessels to stay relaxed even after ejaculating, leading to a prolonged erection.

Injectable medications—where you give yourself a shot of blood-flow boosting meds into your penis’s shaft—come with a slightly higher risk than oral meds. That’s because they’re more powerful than oral meds, Dr. Williams says.

But the real problem comes from using the medications incorrectly, like taking too-high doses or using the drugs if you don’t need them.

“With too much ED medication, the blood keeps flowing in, the blood gets trapped, and the erection doesn’t go away,” says Dr. Williams.

That’s exactly what happened in John’s case. After he experienced the 14-hour erection, his doctor felt the dosage of his injectable medication was too strong, so he tried lowering it.

But he experienced another prolonged erection even after lowering the dosage—this time lasting 7 hours total.

His doctor decided to take him off injectable meds and put him on Cialis instead. He hasn’t experienced any problems since making the switch.

What else can raise your risk of priapism?

But ED meds aren’t the only factors associated with priapism: Certain blood disorders like sickle cell anemia or leukemia can make it harder for blood to flow out of the penis.

In fact, according to the study published in the Journal of Sexual Medicine, 20 percent of guys who went to the ER for priapism had sickle cell anemia.

Some meds for conditions other than ED—like some antidepressants, antianxiety meds, and blood thinners—can also increase your risk, too.

How can a prolonged erection hurt your penis?

Priapism isn’t just uncomfortable and embarrassing. It can also put your penis at risk for tissue damage that can make erectile dysfunction worse, says Dr. Williams.

When blood stays trapped in your penis for too long, it can start to clot, blocking the flow of fresh, oxygen-rich blood.

“When the penile tissue isn’t receiving oxygen from the blood, tissue starts to die,” says Dr. Williams. “That leads to the development of permanent scar tissue that doesn’t function normally anymore.”

As a result, you can find it more difficult to get and maintain an erection in the future.

What should you do if you experience a prolonged erection? 

If your erection isn’t going away after sex or is uncomfortable, it’s okay to wait at home for a little while to see if it goes away on its own, says Dr. Williams.

But 4 hours is your max: At that point, you need to head to the emergency room as soon as possible.

The longer you wait to get treatment, the more likely you are to sustain lasting tissue damage, Dr. Williams says.

Once you get the to ER, the doctors will usually start by giving you a penile injection of a drug called phenylephrine, which tightens up your blood vessels to reduce blood flow to the penis.

“If blood in the penis has already clotted, they may also need to use a needle to flush out the blood clot and get normal, healthy blood flowing back into the tissue,” says Dr. Williams.

John admits having a giant needle injected into his penis was painful and more than a little intimidating.

Still, it’s better than the second-line option: an operation to remove the blood clot, which must be done if doctors can’t flush the blood clot out.

And while he was sore for a few days after, John didn’t experience any lasting problems related to his priapism.

In fact, with fast treatment, many guys will still be able to get an erection with no problem in the future.

“But the best treatment for priapism is to avoid getting it in the first place by taking your ED medications as instructed,” says Dr. Williams.

Additional reporting by Alisa Hrustic

*Name has been changed