Anti-depressants & the inability to orgasm in men?

SSRIs can do this. Anorgasmia means inability to have an orgasm. Ssri antidepressants (prozac, zoloft, celexa, lexapro, (escitalopram) paxil) are well-known to do this, in both men and women, for a sizable minority of patients. The side-effect is temporary (it ends if the ssri is stopped), and sometimes additional meds can be added to counteract this side-effect if the ssri is otherwise helpful.
No O. This is a common reason men discontinue antidepressants. It can help to consider the side effect when choosing the medication. Several do not have as high of an incidence - bupropion, nefazadone, and possibly viibryd (vilazodone hydrochloride). Add ons can work some of the time - bupropion, buspirone. Underlying physiological problems can be worsened with meds. Check testosterone levels. Shortening the time on med helps.
Unfortunate effect. Inability to orgasm is a well known sideeffect of many anti-depressants. Discuss this with your doctor. Hopefully medication can either be changed to one one that does not have the same side-effect or you can slowly be weaned off and no longer require the medication. This should only be done under medical supervision. Good luck.