I've had 3 reclast infusions (2019, 2021, 2023). I was sick for several days after the first, mostly fatigue and joint pain, and 1.5 days for the last two. Those were the only reactions. My osteoporosis was not severe, but it did reverse/stop bone loss. I also do weights and other resistance exercises and take calcium and magnesium citrate. A friend has been on reclast pills for a few years for fairly severe osteoporosis; negative effect is mainly loss of smell and taste. I'd rather be sick for a few days then take pills (the infusion lasts for more than a year at resorbing calcium into bones).