Possible side effect of synthroid (thyroxine)?

Rash: In general, it's a very safe drug. Possible side effect is a rash, caused by the dye used to make the pill color. When this happens, it's recommend to use the white pill to see if the rash goes away. The white pill contain no dyes. If the rash goes away, then it's likely the dye. Other side effects: if use too much: fast heartbeats, shaking, nervousness, diarrhea, headache, insomnia, hair loss.