General principal -- drugs do not deal principally in ability score boosts or penalties (that is secondary, if a factor at all). Drugs should have mechanical effects beyond the banality of numbers (to be interesting).
To better frame my proposal, I would begin by saying that by definition potions are drugs, they just don't have negative side effects. I want to introduce consequences for decisions, which 3.5e is not particularly adept at. Sometimes there is an outside-game reason for that (fun), or the benefits of having mechanics do not outweigh whatever detriments there might be (e.g. time). The drawbacks existing as part of the same function as the benefits makes for a more gray setting, which is something that appeals to me.
- Myconid Spores
- Grants: Telepathy
- Failed Save: Phantasmal Killer / Suggestible
- Active Use: Phantasmal killer
- Pixie Dust
- Grants: Flight
- Failed Save: Personal reverse gravity
- Active Use: Share a few rounds of use with someone, just enough to make them rise and drop (penalty to save, cuts into user's fly time)
- Aranea Eyes
- Grants: Spider Climb
- Failed Save: Cannot drop weapons, become stuck to surfaces