My tsh levels are at a 4.25. i am currently taking 50mcg of synthroid (thyroxine). my doctor upped my dose to 75mcg. i am afraid of side effects like racing heart?

Take it: Adjusting a thyroid medicine is both an art and science. You need to be "euthryroid" meaning normal tsh, t3, (liothyronine) T4 and must feel well as the normal range is made for a population and not your particular body. Fine adjustments must be made between you and a trusted doctor with an aim to make you feel well and healthier and avoid side effects such as palpitations. So go slow.

Recommendation: Just check your thyroid panel within four to six weeks. If you feel your heart racing or palpitations, go to your doctor to get a 12 lead ekg. Make sure you take your thyroid medication early in the morning on an empty stomach.

Unlikely: You won't have side effects as long as your dose keeps your blood levels normal. It needs to be rechecked 6 weeks after you increase the dose. Continue taking the brand name replacement, not generic.

Reasonable: You need more thyroid hormone and the dose increase is reasonable. I would listen to your doc. Just get another lab check in a few months.