In my setting there are various types of magical potions that provide a variety of effects. One of these is a highly potent but dangerous performance enhancer most commonly known by the name of "redknuckle". And one of the many reasons it is so dangerous is because it temporarily enhances the drinker's physical strength, but crucially, not their durability, and it in fact enhances their physical capabilities beyond what their bodies can realistically withstand. People who use redknuckle before getting into fights have a tendency to break their own bones and tear their own skin, hence the name of the potion.
Now, most of the people who use this potion are not mundane mortal humans, so the comparison isn't perfect. However, assuming that the people who use this potion, even if they're stronger and tougher than humans, have a comparable strength-to-durability ratio to that of humans, I'm trying to get a sense of what the minimum effect of this potion would have to be before the potion would get a reputation of its drinkers seriously injuring themselves with their own power.
How much stronger would redknuckle have to make a human before their own punches and kicks, when directed against another human opponent, would be liable to cause them to break their own bones and tear their own skin?