Get emergency medical help if you have signs of an allergic reaction to Synthroid: hives; difficult breathing; swelling of your face, lips, tongue, or throat.
Call your doctor at once if you have:
fast or irregular heartbeats;
chest pain, pain spreading to your jaw or shoulder;
shortness of breath;
fever, hot flashes, sweating;
tremors, or if you feel unusually cold;
weakness, tiredness, sleep problems (insomnia);
memory problems, feeling depressed or irritable;
headache, leg cramps, muscle aches;
feeling nervous or irritable;
dryness of your skin or hair, hair loss;
irregular menstrual periods; or
vomiting, diarrhea, appetite changes, weight changes.
Certain side effects may be more likely in older adults.
Common Synthroid side effects may include:
chest pain, irregular heartbeats;
shortness of breath;
headache, leg cramps, muscle pain or weakness;
tremors, feeling nervous or irritable, trouble sleeping;
increased appetite;
feeling hot;
weight loss;
changes in your menstrual periods;
diarrhea; or
skin rash, partial hair loss.
This is not a complete list of side effects and others may occur. Call your doctor for medical advice about side effects. You may report side effects to FDA at 1-800-FDA-1088.
 Synthroid side effects (more detail)
