Out of the products at iherb.com, this
is the tryptophan I chose. This
is the 5-HTP I might have bought.
Those tryptophan caps do not contain rice flour, but the 5-HTP caps do. I couldn't find any reasonably priced 5-HTP caps that didn't contain rice flour. That's one reason I chose tryptophan over 5-HTP.
The other reason is the chain of conversion: the body can convert tryptophan to 5-HTP, which it can conver to serotonin and melatonin. I prefer letting it decide how much of each it wants to make from a lower level than a higher level.