If you hang around a gym long enough, then chances are, some dude is gonna mention steroids. It’s probably just a joke or a passing reference, nothing to take seriously. And for the most part, nobody worries about it. Nothing to see here. Right? Right.

The reality, though, is a little more grim: Ever since famed slugger Mark McGwire was infamously accused of using performance-enhancing drugs back in 1998, steroid use has not only become a part of the pro game, but also infiltrated average Joe gyms across America. Even though anabolic steroids are technically illegal—the Drug Enforcement Agency busted 16 labs in September, netting tons of tablets and injectable liquid—that’s not stopping everyday dudes from trying to get their hands on them.

That’s right: Everyday dudes. “The main customers for what’s being churned out of the illegal labs the DEA took down are gym-goers who want to get stronger and look different,” ace reporter David Epstein wrote in “Everyone’s Juicing,” a September 2015 exposé for ProPublica.

But while guys are plenty familiar with the supposed “benefits” of steroids, they’re typically in the dark or, worse yet, downright misinformed—about all the nasty side effects they have on your body and possibly even your mind. (And they are nasty.)

To clear up some locker-room rumors you may have heard, we talked to two experts: Dr. Ed Sebanegh, M.D., the department chair of urology at the Cleveland Clinic in Ohio, and Dr. Stuart Weinerman, M.D., an endocrinologist at North Shore–LIJ Health System in New York. We asked them the awkward questions about some persistent steroid myths, so you don’t have to find out the hard way from some jerk at the gym complaining about the sudden emergence of his man-boobs.

RUMOR: Steroids shrink a guy’s testicles.

TRUE. When a guy takes steroids to increase his testosterone levels, it throws his body’s natural hormone balance out of whack, and that manifests itself by shutting down his body’s native testosterone production. End result: Smaller testicles.

“Our body has feedback mechanisms, so it senses a guy’s levels of male hormones and uses that to decide whether it needs to ‘turn down the thermostat,’ so to speak, or if it has enough on its own,” Sebanegh explains. “When a guy uses these drugs, his body ‘turns down the thermostat,’ and it turns off the androgen production in the testicles.’”

In essence, it forces your body’s hormonal balance to a “pre-pubescent state,” he says.

RUMOR: A guy’s testicles will go back to normal as soon as he stops taking steroids.

FALSE. Even after a guy stops taking anabolic steroids, his body will need time to ramp back up to its normal production of its own testosterone. “It’s a general rule of thumb that the higher the dose, and the longer the use of medication, the longer you can have suppression of the gonads,” Weinerman says. “It’s not fully clear if, or how often, it’s permanent in men. But I have seen patients with seriously or severely low testosterone for two years after stopping anabolic steroids.”

In some cases, Weinerman says, guys “can have long-lasting fertility and sexual dysfunction problems” as a result of steroid use.