If you’ve spent at least 10 minutes in a hardcore gym or ever skimmed the headlines of the local sports page, you’re probably aware that anabolic steroids have a reputation for giving athletes a (completely jacked) leg up over their peers.

But how much of an advantage do anabolic steroids really offer? And what’s the biological price of using anabolic steroids to augment your physique? Here’s a deep dive on how steroids work, who’s taking them, how widespread steroids are, and what exactly steroids can do to a man’s body—for better and for worse.

What exactly are steroids?

Anabolic-androgenic steroids are a synthetic version of the testosterone your body already makes. “They look and act a lot like natural testosterone. The hormone attaches to the receptor sites on our cells and affects your systems just as the natural hormone would,” explains Robert Kersey, Ph.D., the director of the Athletic Training Program at California State University, Fullerton, and lead author of the National Athletic Trainers’ Association position statement on anabolic-androgenic steroids. In fact, steroids work so seamlessly that if a guy has clinically low levels of testosterone, a doc may prescribe a type of anabolic steroid to bring his levels back up to normal.

The difference comes when people start “abusing” steroids, or taking far beyond a normal prescription dose. “If a young male were to get testicular cancer where their normal production of testosterone goes way down, a physician might prescribe 5-20mg a day—that means a normal, therapeutic dose is maybe 70mg a week,” Kersey explains. “But for athletes seriously trying to improve performance, they’re probably taking 700-1000mg a week. Some big bodybuilders are taking more than 5000mg a week.” When you start getting over 500mg per week, the side effects start to set in.

How is it sustainable, physiologically, to take such a massive dose? Most heavy steroid users will cycle dosages, either increasing the dose and frequency until they peak, then gradually taper and repeat; or taking large doses over a certain period of time and then pausing for a bit to let natural production start again, until they restart usage.

Who actually takes steroids?

Anabolic-androgenic steroids are the most widely used appearance- and performance-enhancing drugs in the U.S., and are used by everyone from professional athletes to amateurs and adolescents, according to a 2016 study published in FP Essentials.

Steroids are often associated with professional athletes and bodybuilders, but a January 2017 paper published in JAMA reports that 2.9 million to 4 million people in the U.S. have used anabolic steroids at some point in their life, and that nearly all of them are men. What's more, about 1 million American men have become dependent on steroids, using high doses for years, according to the paper.

Steroids aren’t going away, either. Steroid use is increasing, with up to 5% of male and 2% of female college athletes using anabolic steroids, and “a more than 20% usage rate among teenagers,” according to the FP Essentials study.

Where do guys get steroids?

Anabolic steroids are considered a schedule III drug, so without a prescription, they’re considered illegal in America. Steroid use is banned in most sports competitions, like the Olympics, even if athletes have a ‘script.

As for the average joe, getting a doc to write an Rx isn’t as easy as it would be for, say, painkillers. “Not many doctors across the country are going to write prescriptions for anabolic steroids because they’re a schedule III drug,” Kersey says. Some guys even take veterinary-grade steroids, which require a prescription from their vet for their pet.

But the majority of American men who take non-prescription steroids are probably getting their steroids through the Internet via international sellers. And that sets up another problem: Because the steroids are coming from abroad, buyers have virtually no way of verifying that they’re getting a quality product, points out Linn Goldberg, M.D., professor emeritus at Oregon Health & Science University, who co-developed a NIH-sponsored program to reduce drug use (particularly anabolic steroids) among adolescent athletes.

That being said, the U.S. Food and Drug Administration doesn’t regulate supplements, so many over-the-counter products sold in America (let alone online from overseas) actually contain some amount of anabolic steroids, Goldberg says. In 2000 and 2001, some 15% of nutritional supplements purchased internationally (and 19% of supps bought in the U.S.) contained undisclosed anabolic steroids, according to a 2004 study published in the Internal Journal of Sports Medicine.

It’s hard to say exactly how many supplements today contain unlisted steroids or stimulants. Anywhere from 3% to 25% of supplements made prior to 2010 could contain unlisted supps, according to a 2010 review of supplement testing from Informed-Choice.org, a nonprofit service that tests supplements for substances banned in athletic competition. “Guys could be taking low doses of steroids without even knowing it—and oral [supplements] are the worst because they are hardest on your liver,” Goldberg adds.

Why do some guys use steroids?

You already know the stereotypes—and for once, they’re pretty accurate.

“Anabolic steroids are synthetic androgens. Synthetic androgens help men build muscle more easily, burn more fat, strengthen bones, lower their voices, increase facial hair, and speed up balding,” says Goldberg.

There are three main reasons guys start taking anabolic steroids, Kersey says. The first is if a physician prescribes steroids for an actual medical condition—like delayed puberty in young boys, damaged tissue after an injury, or clinically low testosterone. In those cases, men typically do not take steroids at high, potentially damaging doses.

The other reasons guys take steroids? A better physique and better sports performance.

And let’s be clear: High doses of anabolic steroids will certainly help increase your muscularity. Anabolic steroids can increase lean muscle mass if you also exercise a ton and diet properly, according to a 2016 study analysis published in FP Essentials.

“Steroids might affect body mass a number of ways, but the primary way is by promoting muscle protein synthesis,” Kersey says. More testosterone means your body can leverage protein better to build more muscle and burn more fat. But you won’t morph into a giant by ripping steroids from the couch. The effects only hold true if you’re also putting in the physical work to bulk up, Goldberg points out.

When it comes to performance, though, the science of steroids isn’t quite as solid. Steroids do typically improve strength and power, according to a meta-analysis authored by Kersey and a team of researchers. That makes sense, considering steroids help increase muscle mass. But the same study, published in the Journal of Athletic Training, also found that steroids don’t do anything to improve speed or endurance that you couldn’t already accomplish by training clean.

“Do steroids improve performance? That depends on your measure of performance,” Kersey says.

As with any drug, there are side effects. “You may have improved performance, but what about the other side of the equation? Whenever you have ‘good,’ there are always potential problems,” Kersey points out.

And, in fact, even though steroids might help you build more muscle, they may also increase your risk for injury: A whopping 22% of physique-minded lifters who reach for steroids long-term have experienced a tendon rupture, most often in their upper body, according to study from Harvard University. (Compare that to just 6% of clean bodybuilders.)

What are the main risks of steroids?

“I don’t try and hide the positives—steroids can make you bigger, stronger, maybe faster,” Kersey says. “But they also have major side effects, and the damage of these are harder to see than the ‘positives.’”

And he means literally—most of the damage steroids do is internal, so an abuser can go months or even years without realizing the havoc their habit is causing.

Internal risks of anabolic steroids

For starters, steroids can seriously damage your heart. Steroids lower your “good cholesterol,” increase your “bad cholesterol,” and increase your blood pressure and your risk for heart disease, Goldberg says.

In a study of 140 male lifters 34 to 54 years old, lifters who had been using anabolic steroids for more than two cumulative years of their life had more myocardial dysfunction—a level of damage commonly seen after a heart attack. Consistent steroid users also had accelerated plaque in their coronary arteries compared to lifters who had never touched steroids. Furthermore, men who use steroids double the risk of dying from heart disease compared to guys who don’t touch the stuff, according to a study in Drug and Alcohol Dependence.

“In the '90s, when all those wrestlers were dying young—in their 30s or so—a lot of the cases were from heart attacks,” Goldberg adds.

Steroid abuse also makes your blood thicker, so it can increase your risk of blood clots. This puts endurance athletes at an especially high risk, since being dehydrated (like from long, grueling rides) also increases your risk of a clot, and thereby for a pulmonary embolism, Goldberg says.

Then there’s your liver, the primary organ responsible for detoxifying your body.

In a study of young Brazilian bodybuilders (average age: 26) who had used steroids for at least six months, even recreational steroid use led to all sorts of liver problems, including a higher risk for liver disease among guys who didn't even drink alcohol.

“For someone who drinks a beer once in a while, their liver can process that even though it sees it as poison,” Kersey says. “But if he were to drink a case of beer every day for 20 years, his liver can’t keep it up. Abusing steroids has the same effect.” The damage is intensified because most people start off taking anabolic steroids orally (as opposed to via injection), which is harder on your liver.

“Steroids are a drug, and all drugs have side effects,” Goldberg points out. “But these aren't just a drug—they’re also a hormone. When your body senses you have enough of a hormone, it suppresses the pituitary gland and shuts off production of that hormone.”

When you’re consistently dosing your body with massive amounts of synthetic testosterone, your body stops producing testosterone naturally. The main effect of this: Your testicles shrink and you become infertile. In that sense, Goldberg says, “steroids are essentially male contraception.”

While natural production will eventually start again if you stay off of steroids, returning to normal can take months or even years. A Harvard study of former steroid-using bodybuilders who had been clean for three to 26 months found that the now-clean lifters still had significantly smaller testicles, lower serum testosterone, and lower libido compared to guys who had never used steroids.

External risks of anabolic steroid use

Because steroid use floods your body with testosterone, men experience symptoms we usually connect with going through puberty, except even more extreme: acne on the face, back, and chest; mood swings; hair growth in some places; even breast enlargement, known as gynecomastia. While most of these side effects are reversible, gynecomastia isn’t always, Goldberg points out.

Kids who start taking steroids during puberty will also experience stunted growth, because since an overdose of testosterone freezes the growth plate—and that effect is permanent, Goldberg says. They will never reach their full genetic height.

Psychological risks of anabolic steroid use

Because steroids are hormones, steroid abuse has psychological effects. (Hence: Guys who are on a steroid cycle have less inhibition control and are more likely to be impulsive and aggressive than guys who are off their cycle, according to a 2014 study in Psychology of Addictive Behaviors.

“You have hormone receptor sites in your brain as well as your body, so when you throw in 100 times the normal dose of what your body produces naturally, you have extreme changes in behavior and mood. High mood swings, aggression—[use of] these drugs [has] even been used as defense in murder cases,” Kersey says.

Among more than 10,000 Swedes, those who used steroids for years on end—especially in conjunction with other substances like alcohol or other drugs—were significantly more likely to be convicted of a violent crime than guys who never reached for steroids, according to one study published in Addiction.

As for that “roid rage” stereotype: “You’re not going to turn someone who’s docile into a raging nut, but if you’re naturally enraged or have aggression, taking steroids is going to make that a lot worse,” Goldberg clarifies.

One last point: Because steroids have all these side effects, a lot of abusers will then take other drugs to offset the effect—steroid abuse causes you to grow man-boobs, so people take another drug to mitigate those side effects. Guys who take steroids often also take augmenting drugs to decrease estrogen production or to improve athletic performance even further, like human growth hormone, insulin-like growth factor 1, insulin, erythropoietin, stimulants, diuretics, levothyroxine, and/or gamma-hydroxybutyrate, according to the study in FP Essentials. That means on top of all these side effects of steroids, most abusers are also looking at a whole separate list of effects from their peripheral drug habits.

Read more here about the side effects and myths of steroid use.