Steroids seem to have two functions: making people strong and screwing up their lives. We’ll take a look at how steroids accomplish both of these tasks. From bulking muscles to shrinking testicles, this is what happens when you put a steroid in your body.

When people bring up “steroids” while they’re talking about sports, we know what they mean, but the term “steroid” in medicine is so broad it’s almost meaningless. Link twenty-three carbon molecules together in a set of four rings and you’ve got a steroid or a sterol. Bile acid is a steroid, although not a powerful one.

More influential in the body, although still unglamorous, are corticosteroids. These steroids are hormones. They’re are used to treat inflammation, and they’re perfect models for how the nastier steroids work. When the body sustains damage in the form of infection, the inflammatory response kicks in. Chemicals called transcription factors activate certain genes, which produce proteins, which cause blood vessels to dilate (redness), fluid to pour into the area (swelling), and the entire area to heat up (fever). Corticosteroids are hormones that suppress these genes. They bind to receptor sites in cells and essentially turn the transcription process of the genes off. Corticosteroids are in everything from cheap over-the-counter topical creams to heavy-duty drugs that require prescriptions.

The “performance enhancing” steroids, anabolic steroids, work roughly the same way. Like corticosteroids they can be applied topically or injected. Like corticosteroids, they are hormones that regulate how much the body responds to damage. Unlike corticosteroids, they do not tamp down the body’s response. Instead of binding to receptors and turning transcription off, they bind to receptors and turn it up.


When muscles are worked hard they sustain damage. That damage is a signal to rebuild, but also to improve. Cells put out more proteins, building the muscles bigger and stronger. This happens in all healthy human beings, but there are hormones that amp up the natural response. One of these is testosterone. Testosterone starts out as androstenedione, a hormone made in the adrenal glands. It gets converted to testosterone in both men and women, although men have a bigger supply of the stuff, which is why they can generally put on more muscle mass than women. Damage a muscle and the hormone increases protein production, so not only do muscles get bigger, they heal faster. Faster healing muscles means more, and more intense, work-out sessions, which in turn mean that a person with a lot of testosterone going through their system can put on a lot of muscle in a short amount of time.

Human growth hormone, otherwise known as gonadotropin, works the same way. It gives people more hormones, more muscle, and more healing. It has the added benefit of being hard to detect. Natural human growth hormone (HGH) has a mix of molecular weights, while lab-made human growth hormone only has one, slightly higher, molecular weight. The difference is hard to detect at the best of times, and within a few days of ingestion the ratio of the hormones in a person’s body goes back to normal.


For a while, people were getting around the temporary detectability of HGH by collecting the hormone from corpses, but the practice turned out to spread a horrible degenerative brain disorder. That made users balk at using HGH, but it’s one of the few things that did. Anabolic steroids were developed all the way back in the 1930s, to help children with hormonal disorders or people with wasting diseases. Naturally they were popular among athletes, but they weren’t a guarantee of good performance. As late as the 1980s, investigations showed that half of people who took performance-enhancing steroids were getting no significant increased stamina or strength. Was it even worth it?

Anyone following sports in the past decades knows, the answer seems to be “yes.” This accounts for the scare ads—which you can see above—that public health organizations put up in the late 1980s as a failed attempt to stem the tide of steroid use. New designer steroids keep being developed as athletes look for drugs that are better, faster, and more difficult to detect. The most famous undetectable “designer drug” is tetrahydrogestrinone (THG), or “the clear.” The drug was able to connect with more receptor sites than other steroids, making the drug much more potent.

Go to almost any message board frequented by body-builders or other serious athletes and you’ll see testimonials to THG and other steroids. Athletes tend to think that steroids are, if not great, then at least better than losing. Although many disapprove of the banning of steroids in professional sports, even the most starry-eyed user admits there are drawbacks to steroid use.


Hormones, especially hormones like testosterone, don’t just do one thing. A build-up of testosterone causes both balding and body hair growth, acne, and extreme mood swings. But the re-onset of puberty (at least male puberty) doesn’t explain the two most infamous side effects of steroid use—growth of breasts and shrinking testicles. How does a hormone that is meant to turn boys into men do that?

When the body gets massive injections of testosterone, it temporarily stops developing any of its own. If the testosterone is on a constant drip, this might not be so bad, but most steroid users inject and then stop, inject and then stop. The body stops producing testosterone, but it goes right on producing estrogen, and this is what circulates in the body between testosterone injections. The predominance of estrogen causes breast tissue to develop.


Then again, a constant steroidal testosterone drip would cause other problems. Steroidal hormones suppress follicle stimulating hormones and luteinizing hormone, both of which stimulate the testicles. Without these hormones, the testicles shrink down. (one man who was prescribed steroids as medication described his as “grapes” and complained about how much loose skin was left over after they shrank) This is often reversible, but only after the steroid use stops. So even under ideal circumstances, people would have to make the choice between small testes or big breasts.

Top Image: Boemski.