What is the difference between Effexor and Prozac?

Prozac (fluoxetine) and Celexa (citalopram) have the same mechanism of action. The biggest differences are in pharmacokinetics (how the body handles the drug). Fluoxetine stays in the body for a couple of weeks after the medication has been discontinued. Citalopram is cleared more rapidly. Fluoxetine has much more drug/drug interactions which might become a problem when using certain other drugs at the same time.