Panic attack after starting Effexor

Although drugs such as Effexor are prescribed for anxiety, it is not uncommon for the serotonin based antidepressants to precipitate serious panic attacks when they are first started.  The marijuana probably also played a role in this panic attack, as both the marijuana and the Effexor affect the autonomic nervous system.  Many people are able to use marijuana and antidepressants, but it was probably worse for you since you had just started the Effexor.  Often the serotonin based antidepressants are initiated along with a benzodiazepine such as Klonopin or Ativan to prevent the initial anxiety/panic that may occur.  It was probably a good idea for you to stop the Effexor, as you likely would have had more panic attacks.  This is a pretty common side effect.  You can still take this category of medicine.  One strategy to prevent initial anxiety/panic is to start off at a very low dose.  Another strategy is to start the medication with a benzodiazepine.  You should avoid marijuana at least until you are stable on the medication.