The manufacturers of Effexor don't recommend it and it would most likely increase the side effects of the Effexor. I wouldn't risk it. Both drugs affect the nervous system and you don't want to mess with that. Be careful with Effexor - I used to take it and the withdrawal was horrible when I came off of it. Also, as I think Phentermine is a weight loss supplement, I now take an anti-depressant called Wellbutrin which is Bupropine - it's excellent and one of the side effects is weight loss. It's another antidepressant so you probably should not take both but your doctor or pharmacist would know best on that front. So the short answer to your question - Probably not smart.

Phentermine and effexor are great together! It actually makes the phentermine work better. You will loose more weight more quickly and not have those cravings. There are several weight loss doctors that prescribe both of these drugs together for this purpose.