High

Is it true that when you are lucid you can become stoned in your dream?

Welcome
Yes, this can also happen in a non lucid dream, though. I know only the non-lucid stoned, which feels a bit different than when awake. Less effects on your thoughts and more optics I´d say

tapir

P:S: I think somewhere is a whole thread about drugs in dreams, use the search if you are interested

Yes, it’s possible. In an LD you could make a magic pill appear and tell yourself ‘this will make me feel stoned’. Then it depends how much you expect/believe it to work.