I took 7.5 mg of synthroid (thyroxine) 3 days ago. i have been experiencing palpitations, racing pulse, headaches. will it get worse?

Are you sure?: 7.5 mg = 7, 500 mcg! the usual dosage of synthroid (thyroxine) is 25-200 mcg. 7.5 mg would be life threatening! were u taking Armour Thyroid or some other form? If it was synthroid (thyroxine), was it possibly 75 mcg? Synthroid (thyroxine) should be started at 25 mcg/day, and gradually increased to the target dose, like 25 mcg/day increase every 4 weeks. You should stop if you get racing heart or chest pain (from the pkg insert).