Insulin (performance use)

The verdict

Our read at a glance.

Whether exogenous insulin adds muscle in people who are not diabetic, and whether any plausible benefit survives the hypoglycaemia risk.

The signal

Insulin's approved role is the treatment of diabetes, and that evidence base is enormous and unambiguous. What does not exist is evidence that adding insulin to a healthy, non-diabetic person builds muscle. Its anti-catabolic and nutrient-partitioning effects are real biochemistry, but in a healthy person the pancreas is already producing insulin in response to food, and the marginal benefit of exogenous dosing has never been demonstrated in a controlled trial. The literature that does concern this population is clinical toxicology: case reports and series of severe hypoglycaemia, coma, permanent neurological injury and death in bodybuilders using insulin, alongside the forensic problem that insulin is difficult to detect postmortem.

The unknown

Nothing about the risk. What is genuinely unknown is whether there is any anabolic benefit at all in a well-fed healthy person, and no one is going to run that trial.

Our read

The clearest risk-versus-evidence mismatch on this Watchlist. Real, life-saving drug; zero evidence for the use it is being put to in this population; and a failure mode that can kill someone in their sleep before anyone notices. Being biochemically anabolic is not the same as being shown to build muscle in someone who already makes their own.