Which is that I would like him not to do it. At all.
He isn't an addict. He takes ecstasy and ketamine a few times a year when clubbing with friends, and smokes weed about as many times. It isn't often.
Firstly, dabblings in drug-taking should end when kids arrive, surely? Secondly, DP has a recent history (not from when we first got together) of alternating periods of depression and hypomania. He has evaded a diagnosis of a mood disorder, but displays many of the symptoms. And to my knowledge, recreational drug-taking is a bad idea for anyone prone to mood extremes.
Drugs don't appear to be a direct trigger for DP's up and down moods. But I feel that, particularly because he doesn't take medication, DP should do all he can to self-manage responsibly, and this would include eliminating or reducing even potential triggers from his life. Plus, we don't know what the latent effects of drug-taking could be. Hence, I think his taking these drugs while staying up all night clubbing and depriving himself of sleep, however infrequently, is unacceptable. (And the sleep deprivation is significant for him).
AIBU and a control freak, or - given the past and potential effects on me and family members of DP going up/down - am I well within my rights to insist he steer clear? He thinks he's managing the risk just fine, and I'm not convinced.