Hi Laura,

Thanks for your question. Taking these two medications can potentially cause harmful side effects, so I'm glad you asked. Two or three days should be enough time for the Effexor to clear out of your system, and then you can start taking the Celexa. Even so, if you experience any of the following symptoms be sure to contact your doctor immediately, as these are symptoms of serotonin syndrome (a rare but dangerous condition): racing heartbeat, excessive sweating, shivering, twitching, and overactive reflexes. Serotonin syndrome can occur when taking two or more medications that both affect serotonin levels in the body. You can read more about serotonin syndrome here.

Best of luck,

Casey