If you've smoked weed in real life then it will feel the same while Lucid.
If you haven't your brain will give you a feeling it imagines smoking weed would feel like.

Funnily enough in a really vivid non Lucid last night, where I was at a party at a Friends who I haven't seen in years.
I didn't actually take them in the Dream but could tell from how I felt, that I'd taken way to much Ecstasy, again something I haven't done in years and that felt completely real.