S-40503 Reference

Plain English

What it is

S-40503 is a SARM, which is a lab-made drug that targets the body's muscle- and bone-building hormone signals. It was created as a research compound to study bone, and it is sold as a research chemical, not as an approved medicine.

What people use it for

In the bodybuilding and body-recomposition crowd, SARMs get used to try to build muscle and lose fat, based only on personal stories and not on any approved medical use. Real-world use of S-40503 itself is essentially nonexistent; it mostly turns up in long lists of SARMs because of its bone claims, which have not been shown to work in people.

What the science shows

The published research on S-40503 is animal-only, mostly rat studies of weak bones (osteoporosis) that suggest it can build bone without enlarging the prostate. It never moved into human trials, so there is no proof of any benefit in people.

The catch

The FDA has warned the public that SARMs are not approved, are sold illegally in bodybuilding products, and are often mislabeled, and global sport rules (WADA) ban SARMs at all times as anabolic agents (class S1.2). Across SARMs as a group, real risks include lower natural testosterone, liver strain, and drops in good (HDL) cholesterol that can affect the heart, and none of these have been ruled out for S-40503.

Reference summary

Published evidence is animal-only, mainly rat osteoporosis-model work suggesting bone-anabolic activity without prostate stimulation. Human evidence is absent.

Regulatory and posture

Categories

SARM, Bone

Aliases

S40503, Bone-anabolic SARM, Non-steroidal SARM

Evidence posture

preclinical - Animal-only bone SARM prototype. Human osteoporosis, fracture, or performance benefit has not been shown. WADA-prohibited; no FDA approval.

Regulatory status

No FDA-approved S-40503 drug label. FDA consumer warnings against SARMs sold in bodybuilding products apply to the class. WADA prohibits SARMs under category S1.2 anabolic agents at all times.

Content review status

research reference