Does dosing by weight vary between types of molecules?

I learned in pharmacology that most drugs should be dosed by weight and anesthesiologists are always doing this but it's too complex for the general public so with things like aspirin and Tylenol and prescription drugs they just generally give average safe dose guidelines.

Someone asked me if MDMA, because it acts on the brain more rather than the entire body like an anti-inflammatory such as ibuprofen, if that meant the dosing didn't matter as much for a small person versus a big person? I have no idea so I wanted to ask here. A lot of the toxicity studies that MAPS did we're done at milligrams per kilogram.

For example, if a 100 lb woman and a 200 lb man both take the exact same dose would the larger man feel the effect less? I don't think the logic of it working mainly on the brain is correct because it still spreads throughout the entire body and there's lots of receptors in the gut for example. So that same amount gets spread thinner in a 200 lb man than a 100 lb woman and I assume would therefore lead to less of an effect. Any insight on this?