Substances used as both drugs and flavorings

How many substances are there that can be used in very small amounts as a flavoring in food/drinks, or in larger amounts as a drug?
Two obvious examples I can think of are caffeine and methyl salicylate.

Caffeine is bitter. It’s not added for flavor.

Do you count things like vanilla extract? The flavor doesn’t come from the alcohol itself; that’s just used as a solvent for the flavor. But there’s still alcohol in it, and enough of it would still make you drunk (with really nice-smelling breath).

Nutmeg. The psychoactive effects are not particularly pleasant, but it has been used by people who are desperate for some kind of buzz, like prison inmates.

Ginger is a well-known natural remedy for sea-sickness.

Would you count wine?

Quinine is the flavoring in tonic water and also an antimalarial drug.

Another bitter substance. I know there are people who like tonic water for some reason that non-psychotic people don’t understand, but the Gin and Tonic drink was designed to kill the horrid flavor of quinine.

How about poppies? The seeds aren’t what’s usually used for making opium, but there are still trace amounts in them.

Bergamottin could loosely fall into this category, although I don’t specifically know exactly how much bergamottin itself contributes to the flavor profile of bergamot essential oil. Aside from the uses outlined in the wiki article, I’ve also occasionally seen references to the possibility of deliberately using the grapefruit juice effect to partially mitigate the cost of expensive drugs to low-income consumers. People who abuse benzodiazepines for recreational purposes are known to concurrently ingest grapefruit juice for its inhibitory effect on the CYP3A4 enzyme.

Coffee, Tea, Chocolate, Beer, Broccoli, Greens… I’m not sure why you are starting off with the assumption that bitter is not a flavor.

Yeah, I don’t get it, either. Bitter is definitely an important flavor component and enjoyed by many, even in other commercial soft drinks like, say, Moxie. That said, I don’t think the caffeine in cola is there for flavoring in the way it is in tonic water. I assume it’s just there for the “perk.”

Turmeric is the spice used in curries as well as mustard. It contains curcumin, an anti-inflamatory among other things.

Cloves…

I’m not saying bitter isn’t a flavor, I’m saying caffeine isn’t added to get a bitter flavor, it’s added as a stimulant.

Speaking of bitter, we have Angostura bitters, now used to flavor cocktails, but originally sold as a medicinal tonic.

Aspartame (NutraSweet) was originally discovered by a pharmaceutical chemist who was working on a drug for treating stomach ulcers. Probably doesn’t actually count as a “drug”, however.

But quinine is definitely added to a Gin and Tonic to make it taste like a Gin and Tonic.

And in fact, the bitterness from caffeine in cola can’t be detected in blind studies:
http://www.sciencedirect.com/science/article/pii/S0195666306006507

Subjects could distinguish between caffeinated and non-caffeinated sweeteners (p <0.001), but all subjects failed to distinguish between caffeinated and non-caffeinated cola beverage (p=1.0). Caffeine has no flavor activity in soft-drinks yet will induce a physiologic and psychologic desire to consume the drink.

Admittedly, this still doesn’t prove that it isn’t added as a flavorant. It could be added for that reason even if the reason is invalid. I wonder what the regulatory argument is (flavor with a side effect of stimulant seems an easier sell than additive for the sole purpose of stimulant).

Supposedly, though, the gin was added to make the quinine water palatable. I would almost say it works the other way 'round, too, that tonic water is added to gin to make it palatable. I’ve since developed a taste for gin, but for the longest time the only way that I could find either gin or tonic palatable was in a gin and tonic. There is just something truly magical and synergistic about that combination (well, and lime, of course.)