In the 60's to 1989 research into tryptophan grew rapidly, millions used it for depression. In 1989, a contaminated batch forced the FDA to pull tryptophan off the US market, never to return. This destroyed all research into this critical amino acid and cleared the way for pharmaceutical drugs and billions of profits for them. I am asking the question, why do so many drugs work on the tryptophan oxygenase (pyrrolase) pathway? We have antidepressants (all classes). Related articles; http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=pubmed&dopt=Abstract&list_uids=7126996 And here; http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=pubmed&dopt=Abstract&list_uids=1826617 Then we have alcohol; http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=pubmed&dopt=Abstract&list_uids=10721064&query_hl=9 Then we have asprin; http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=pubmed&dopt=Abstract&list_uids=7082905&query_hl=15 Nicotine, morphine, phenobarbitone http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=pubmed&dopt=Abstract&list_uids=989&query_hl=17 then we have...