system
Given the following post, respond as if you're commenting on Reddit:
human
If amphetamines and opiates both work by overstimulating dopamine production, why are their effects on the body almost polar opposites?
gpt
I know this one!! Amphetamines work by not letting dopamine neurons suck back up dopamine (i.e., it is a dopamine reuptake inhibitor). Thus, the dopamine stays in the spaces between neurons for longer, giving it more opportunities to bounce around and activate other stuff. This is what causes the "upper" feeling.

Opiates work by activating opiod receptors that kill pain. Yes, it does cause an increase in dopamine as well, but that's more of an after effect of activating the opiod receptors. In other words, the increase of dopamine is not that important for the painkilling effect of opiods, whereas dopamine is the whole basis behind amphetamines.