@Ailbhe L-phenylalanine is what you get if you take amphetamine and replace the alpha methyl group with formic acid. It's an amino acid that is used as a precursor for all sorts of stuff the body does with substituted phenethylamines. In particular, it makes dopamine from it, via a few extra steps. Raw material basically, It's listed because there's a condition called PKU which is very very rare but involves being unable to metabolise away a lot of substituted phenethylamines and so if you have too much in your diet you can end up with dopamine poisoning.

It's stupid rare tho.

Anyway, for us ADHDers, it can often massively amplify the effect of amphetamine.

Basically, we can use it recreationally when we're medicated and get high from diet pop.

Don't keep doing it daily though, or it'll stop working.