Can effexor (venlafaxine) cause breathing problems?

Depends: In very very very rare cases your muscles can stiffen up and cause you to feel like you have breathing problems. Usually, you develop breathing problems from having anxiety. It is important to be able to tell your doctor what kind of breathing problem you are having.

Dyspnea or not?: There have been patients that develop a catch in their breath while on medications. In addition a more central problem can occur where one seems to almost forget to breathe. Ssri's and snri's (like effexor) seem to not infrequently cause this. Decreasing the dose typically does not eliminate it. It usually does not occur with all the other agents in these classes - you will find one that does not.