I have had 4 rounds so far. I alternate arms each time, take antihistamine and Tylenol prior to injection to combat site inflammation, and the nurses inject very slowly. No more painful than most injections if done well. I have suffered no obvious side effects that I can pinpoint, other than a little headache the day of or following for which I just take Tylenol or ibuprofen. The website makes it sound much scarier than it is! Good luck!