What is the principal side effects of synthroid ?

Side effects: There usually are not many side effects of Synthroid. If the dose is too high however, then you may have weight loss, agitation, tremors, looser stools, sweating.

Faster heart rate: There are a number of possible side effects, and they may be indicative that the dose is too high (although a lab test should be used to confirm whether it’s too high), which include: faster heart rate, sweating, diarrhea, insomnia, or heat intolerance. Let your doctor know if you experience any of the following: chest pain/tightness, decreased urine production, or fainting.