Just because something is over-the-counter or an herb doesn't mean it can't cause side effects! And sometimes the side effects can be very serious.
I speak from experience. Like a stupid person, I once decided to discontinue an AD I was on to take St. John's Wort instead. I felt great the first couple of weeks, but then I was flying high! It put me in a manic stage (I couldn't sleep at all and was going 90 mph.) That's because I had bipolar disorder, which, at the time, I was not aware I had.
Yes, these things can alter your body chemisty---and mess you up big time. Please use precautions---or better yet, speak to your doctor about them first. I wish I had!