Read the possible side effects in the package insert, I am sure it is a common side, as is reduced libido..........
St. John's Wort has been used in clinical trials and found to work just as well as three of the most commonly prescribed anti-depressants, but without the side effects.
The effective dose is 1500 mg/day, and you do need to get this herb from a reputable source.
If you are considering switching, you have to come off of one before you go on another anti-depressant, even if it is herbal.