Not all meds work the same for everyone. You might be better off with a different drug. I take Prozac and have for many years. They tried to switch me for pregnancy and just for a break, paxil was ok and Effexor did nothing for me.
website says: Panic Disorder. The recommended starting dose is 37.5 mg per day of Effexor XR for 7 days. Patients not responding to 75 mg per day may benefit from dose increases to a maximum of approximately 225 mg per day, o you can increase but it also can take time to see the benefits as you build up.