I have heard all kinds of bad side effects like serious fatigue,breast lumps,high fevers,nausea,arm pain,muscle pain etc.
I'll add that there are things you can do to lessen side effects...yes, some of it may happen regardless, but boosting your odds are always helpful (both for the actual science and the placebo-effect). Hydrating is the best thing you can do, drink lots of water and electrolytes (1-2 days before and after). Stay away from alcohol (or anything that will dehydrate you). Get your blood flowing in your arm before and just after. Continuing to use and move your arm if it becomes sore. Cold compresses help too. And over the counter pain relief as needed (if you're not allergic or have reactions, of course).