With psychedelics some refer to a "museum dose" — that amount you can use that would allow a person to visit an art museum and enjoy the experience. There are similarities with cannabis and other drugs (including alcohol of course).

That said, sometimes a little dab is enough to throw things off — fun story: I was practicing the Filipino Martial Arts and my teacher had a hit off a blunt some fellows practicing kinda-wushu in the same park were passing around. His ability to count out our drills went to hell, but in generally all other ways he was fine. It was very humorous at the time.