I don't quite think "positive" fits in that context. It is a positive thing for someone not to do those things, but it doesn't make them "positive." For a person who does not do any of that stuff, you could call them "straight-laced" or "boy scout" or even "saint". But take in mind these are mostly with a slightly teasing or even sometimes negative when said to someone. Usually it's the people who are doing drugs, drinking, etc.. that tease the person not doing them by calling them these terms. Even more so that the person might change their mind and join in on the activities. Example: Person A: "Hey bro, let's have a drink tonight! First round's on me!" Person B: "Sorry I can't drink tonight, I have to be up in the morning for work." Person A: "Oh I get it, this boy scout over here is too good to drink with us. He's afraid he'll get his hands dirty. A regular Saint Nick." Something like that.

The word 'positive' in context of drug taking would normally mean that someone DOES use. This is because if someone who has used a drug is tested for that drug, then the test will give a positive finding and the person might be said to be positive. It would be more common to say that a non-drug user was 'clean'. A non-drinker might be 'dry' or 'teetotal'

slang, and this is actually used, is "straightedge". means someone young who doesnt use drugs or drink alcohol.

“teetotaler” and “nondrinker” both describe someone who doesn’t drink alcohol. They don’t specifically cover drugs, but it would usually be implied. I would say they are neutral words, especially “nondrinker” A similar word is “abstainer” (noun) or “abstinent” (adjective) which I think is more likely to arise in situations where the behavior is motivated by religion. But that wouldn’t necessarily be limited to drugs/alcohol and could include other practices considered sinful. But these aren’t slang. I’d go with Luke’s suggestion of “boy scout”

Dull?