Sorry to revive a long-dead discussion. But if the OP is still around (probably not as I see he's not been active), just wanted to add my two cents - I get the same thing from speed (racemic amph). Thought it was a GI reaction, eg irritating stomach lining, so started plugging it, but still get the same reaction (although a bit less severe). Very annoying, and doesn't feel healthy.
Clearly this is a pharmacological issue if injecting has the same effect. Heard somewhere that amphetamines decrease blood flow to the stomach, and I assume ritalin has a similar effect - maybe something to do with this? .
By the way I do take omeprazole daily (only 10mg but enough to stop any GERD), so that's no cure. Might look into other options, eg liquid suspension suggested above. Anyone else get this? Any other suggestions?
To the person above who asked why he's shooting ritalin...errrrr, probably to get high? Not that it is something I'd do myself!