As long as everyone involved consents and isn't coerced, it sounds ethical and entertaining to me.
I imagine that many of the people who would participate are already taking these things (these are not the people competing professionally today). Perhaps mainstreaming it would incentivize more research into safety and sustainability around artificially pushing humans beyond their current physical limits.
> As long as everyone involved consents and isn't coerced, it sounds ethical and entertaining to me.
Given the extreme competitive and monetary pressure already involved in sports, as well as expectations of audience, I question how much we can talk about consent and lack of coercion. If a drug league would exist, players would be pressured to take part to the very limit of what's legal, health be damned - as they already are in regular leagues.
Drug league could have people dying mid competition, as they took too many drugs that they had a heart attack when trying to go all out, and that would create so much backlash and vicarious trauma that it gets shut down hard. I think it's the main reason why it doesn't exist.