Venlafaxine can interact with L-tryptophan; the Effexor website says to tell your doctor first if you take it.

"Before taking Effexor, tell your doctor if you are using any of the following medicines:

cimetidine (Tagamet, Tagamet HB);

warfarin (Coumadin);

ketoconazole (Nizoral);

tryptophan (sometimes called L-tryptophan);

haloperidol (Haldol) or risperidone (Risperdal);

almotriptan (Axert), frovatriptan (Frova), sumatriptan (Imitrex), naratriptan (Amerge), rizatriptan (Maxalt), or zolmitriptan (Zomig); or

any other antidepressants such as amitriptyline (Elavil), amoxapine (Ascendin), citalopram (Celexa), clomipramine (Anafranil), desipramine (Norpramin), escitalopram (Lexapro), fluoxetine (Prozac), fluvoxamine (Luvox), imipramine (Tofranil), nortriptyline (Pamelor), paroxetine (Paxil), protriptyline (Vivactil), sertraline (Zoloft), or trimipramine (Surmontil)."