[jheriko]

I'm not sure you can describe an essential amino acid as an addictive substance... sure there is a strong desire to consume it, but its closer to things like oxygen, water or any vital thing that keeps you alive.

Caffeine on the other hand has a well understood and documented mechanism of physical dependence, but its considered extremely mild compared to substances traditionally considered addictive (nicotine, alcohol)...

[gojomo]

Do people crave phenylalanine beyond the essential levels needed? There's strong hints some do, via both diet sodas and sugar-free gums. And there's a plausible mechanism, given phenylalanine's relation to key neurotransmitters, and its use in treating depression and other neurologic disorders.

(I suppose we could raise the same question about food in general. Obviously food is necessary, but can it ever make sense to talk about a 'food addiction'? Or perhaps more accurately, an 'overeating addiction'? I think it can, in some cases. For someone wondering why they feel 'addicted' to diet soda, the high levels of mood-altering phenylalanine from the aspartame is highly likely to be a factor.)

[jheriko]

we are still comparing apples and oranges even with your argument...