I've noticed that oral amphetamine feels different than parenteral ROA. It is more relaxing euphoria, much more empathy and pleasant goosebumps all over the skin. I used to take 5-htp and l-tyrosine, so I can imagine what serotonin/dopamine feels like. My guess is that ingested amphetamine can be oxidized by gastric juices, which changes its pharmacological profile. People taking antiacids before taking amphetamines reported less euphoria and more side effects, which partly confirms the above. The second option is first-pass metabolism, in which part of the amphetamine is metabolized immediately, and not over time. What do you guys say?