Why is insulin misuse dangerous?

Short answer

The muscle benefit is small and the low blood sugar risk is large. Insulin did not increase muscle building, and 56.8% of 41 users had low blood sugar. In 45 overdose cases, 1 in 3 ended up in intensive care.

Why is insulin misuse dangerous?
'Insulin → nutrients pushed into muscle → more muscle' — does this formula hold?
Insulin is a hormone that lowers blood sugar. Some people without diabetes use it alongside steroids to build muscle. We checked what it actually does to muscle, and what it costs.
Do people actually use it?
1 in 4 steroid users
In a survey of 500 steroid users, 25% said they also used growth hormone and insulin. Among 41 people using insulin without diabetes, 95.1% also used steroids, and they used an average of 16.2 different drugs a year.
Does it build more muscle?
Muscle building did not increase
An analysis that pooled 25 studies (173 people) where insulin was given into the bloodstream found that insulin did not increase muscle building. It reduced muscle breakdown instead. Muscle building rose only when amino acids (the building blocks of protein) were raised too.
So is more insulin better?
After a small rise, nothing improved further
8 people received the same amino acids while their insulin level was raised in 4 steps. The first step cut muscle breakdown in half, but raising insulin 2.4 times and 5.6 times higher than that cut it no further. Muscle building did not differ at any step.
The cost is low blood sugar
8% of users had it
Of 41 people using insulin without diabetes, 56.8% had low blood sugar, and 1 lost consciousness. One bodybuilder who secretly injected insulin fell into a coma from severe low blood sugar and needed repeated glucose drips to wake up.
What happens with too much?
1 in 3 ended up in intensive care
An analysis of 45 insulin overdose cases found that 44 were hospitalized, for a median of 94 hours (about 4 days). 15 cases (1 in 3) went to intensive care. 9% had heart problems such as irregular heartbeat, 7% had impaired brain function, 1 person was left with brain damage and 1 died.
Across more cases
About 3 in 100 died
Of 160 insulin overdoses reported to a poison center, 75 had known outcomes: 94.7% recovered, but 2.7% were left with brain damage and 2.7% died. In 3,462 people with diabetes, a single episode of severe low blood sugar was followed by a 2.24 times higher risk of death.
Summary: small muscle benefit, big risk
The formula breaks at 'insulin → more muscle'
Insulin did not increase muscle building, and its effect on cutting breakdown stopped growing after a small rise. Meanwhile 56.8% of 41 users had low blood sugar, and 1 in 3 overdose cases ended up in intensive care.