Zonxx
Bluelighter
actually. Amps can REDUCE, contraction of the G.I tract.Nah like others have said above it's due to the chemicals stimulants release in your brain. Amphetamine does not "shrink your stomach" this would be impossible. It reduces appetite like any stim, but this is done by affecting how your brain perceives food and desires to eat, not changing your body.
In fact ironically I get the munchies from amphetamine recently... it feels as if my body is saying "if you want me to give you this extra energy I need more food."