I was walking through my local supermarket today and I saw generic pill bottles labeled as Zinc, Potassium, Selenium and others. The fact that the store sells them for less than 10$ made me wonder if they would be practical for experiments. I highly doubt this but, are they equal or substantially good in substitute for reagent grade chemicals?

Well, they are salts/complexes of the named metals, combined with various inactive fillers and binders.

If you have a use for the actual salt/complex and a method to remove the filler, go ahead and use them...

Just don't think you can grab some "zinc" pills and use them in place of zinc metal...

Vitamins and supplements can on occasion be a useful method of acquiring a specific chemical; the obvious example being para-amino benzoic acid being the primary precursor in the synthesis of benzocaine, and it being sold pure(ish) and cheap as a dietary supplement. I don't think you'll get common lab reagents out of 'em though.

Niacin > Pyridine is a good one. GABA and Phenylalanine, also handy.

As is tryptophan/5-htp, and (apparently) Coenzyme Q10.

You could use them for electrochem....

Health stores are one of my favourite palce to stock on on nice stuff, you would be suprised what there is! For example as we all know ephedrine is hard to get or to extract, but i walked in this little asian medical herb shop and bought 500 g of ephedra for little under 50 € and no question asked , its a nice addition to your tea and ephedrine can be extracted relaivtly easly from it (althought it appears to be a lot more hygroscopic for some weird reason). Anyways off the top of my head here is what i have found which are good to have around:

5-htp
melatonin
tryphorphan
PABA (para-aminobenzoic aicd)
Niacin
Phenylalanine
GABA

I will add more later on, but these are the main ones

When niacin is purchased, isn't it mixed in with binders/fillers? Wouldn't it have to be sourced pure (or easily pullable) to be usable?
I havn't been following this recently. Is there now a Phenylalanine ---> Amp write-up?

His list reminded me more of JP's phenylalanine stuff a while back, but Im probably wrong.

Not really, more or less, between WD and SM there is quite a bit of work being done on it

True, but it ain't no copy paste, JP had folic acid and assorted other stuff in his