I am currently taking Prozac for depression. Would frequent marijuana use affect how the Prozac works? Is it dangerous?

Taking two different drugs which both cause changes in the brain chemistry is potentially dangerous. Exactly what can/will happen is not easily predictable. Nobody ever has (or ever will) done a study where both marijuana (or any other illegal substance) and Prozac were given and the effects studied. I would strongly encourage you to stop the marijuana, and/or speak to your physician for more details.
                                                                 (01/2006)