What are SARMs (selective androgen receptor modulators)?

In one line

SARMs are unapproved experimental drugs designed to fit the same spot as male hormone but act mainly on muscle and bone.

What are SARMs (selective androgen receptor modulators)?
The name that comes up alongside steroids
In talk about muscle drugs, SARMs come up often alongside steroids. More and more people who work out are using them. But what exactly are SARMs, and how are they different from steroids?
In short
Experimental drugs designed to target muscle and bone
SARMs are drugs designed to fit the same spot as male hormone (the body's signal substance that builds a male body) but to act mainly on muscle and bone. They have been developed since the early 2000s, yet no country has approved them as a medicine for people. They are still drugs under research.
What the name means
Selective androgen receptor modulators
SARMs stands for 'Selective Androgen Receptor Modulators'. 'Androgen' is the group name for male hormones such as testosterone, and 'receptor' and 'selective' are explained in the next cards.
What is a receptor?
A lock that a hormone fits into
Hormones such as male hormone travel through the blood and pass signals to cells. Cells have spots where only a certain hormone fits; these are called 'receptors'. When male hormone fits the 'androgen receptor' like a key, a signal switches on inside the cell.
What 'selective' means
Trying to switch on mainly the muscle and bone signal
Anabolic steroids switch on signals wherever there are androgen receptors: not only in muscle but also in skin, the liver and other places. SARMs were designed to switch the signal on strongly in muscle and bone and less elsewhere. That is why they are called 'selective'.
A different shape
Drugs without the steroid shape
Steroids are substances with a shape made of 4 rings joined together. SARMs are built with a different structure, so they are classed as 'nonsteroidal' drugs. Even with a different shape, they fit the same androgen receptor.
Why they were made
To treat diseases that waste muscle
SARMs have been studied as a treatment for people whose muscles and bones weaken from diseases such as cancer or osteoporosis. So far, there is no clear evidence that they work better than existing treatments. All SARMs today are research-only.
Liver, tendon and other damage
Liver damage was reported most often
Many cases of liver damage after using SARMs have been reported, and the typical sign was 'jaundice', where the skin and the whites of the eyes turn yellow. In a review of cases in healthy people, liver damage was the most often reported problem. Cases of torn tendons and severe muscle damage have also been reported.
Male hormone drops
The body makes less of its own
SARMs also lower the male hormone the body makes on its own. Even in a short trial in healthy people, their testosterone levels fell, and returned to normal after stopping.
Not what the label says
Only about half contained SARMs
When products sold online as SARMs were bought and tested, only about half actually contained SARMs. Most of the rest contained other unapproved drugs. Fewer than half had the amount stated on the label.
Common misconception
They are sold like supplements, so are they legal supplements?
No. SARMs are experimental drugs that no country has approved for use in people. In the US, selling SARMs in dietary supplements is itself illegal, and in sport they are banned at all times.
Summary
Unapproved drugs designed to target muscle and bone
SARMs are nonsteroidal drugs designed to fit the androgen receptor but act mainly on muscle and bone. They are sold like supplements, but they are experimental drugs never approved for use in people. Related terms: anabolic steroids, androgen receptor, the World Anti-Doping Agency prohibited list.