I have a suggestion.
To make it so the drugs aren't pointless to buy, you should make it so you can get addicted to them. What I mean is when you have taken drugs for a certain amount of times, and then suddenly stop taking them, your player goes through withdrawal. The 'withdrawal' could be:
>Your player's speed decreases (this can include jump height)
>Your hunger decreases quicker (your hunger bar goes down 2, maybe even 3, when you haven't had drugs in a while)
These are just two examples, though. Whatever you choose to be the withdrawal symptom, it needs to be something that will actually make a player have to buy more drugs. When the player starts going through withdrawal, it needs to affect them negatively enough to where they need to get more drugs.
Hopefully this hasn't been suggested yet because I haven't read all of the posts.