No side effects. I just wanted to reassure all these people that are unsure about taking Synthroid, that it is the best medicine I've ever had to take. Two years ago, my hair was falling out in big clumps, I had all the symptoms of menopause-night sweats, mood swings, sleeplessness, etc. and my doctor tested my thyroid and found that I have hypothyroidism. It took a few months to get the dosage correct, but I have felt wonderful ever since and I also have all my hair back!