Westhroid Side Effects: What to Expect and When to Call Your Doctor

Westhroid is generally well tolerated when taken at the correct dose. Most side effects occur when the dose is too high—essentially mild signs of hyperthyroidism (too much thyroid hormone). Here's a practical guide to what's normal, what's concerning, and when to contact your doctor.

Common Side Effects of Westhroid

The most commonly reported side effect, especially when starting Westhroid, is:

Temporary hair loss — this often occurs in the first few months of starting thyroid therapy or after a dose change. Hair typically regrows as the body adjusts. This is not unique to Westhroid and happens with all thyroid medications.

Initial changes in weight — as thyroid hormone levels normalize, weight may change (often in the direction of health). This is an expected effect, not a side effect per se.

Increased energy — many patients experience improved energy levels as hypothyroid symptoms resolve. This is a desired outcome.

Signs Your Dose May Be Too High

Most troublesome side effects of Westhroid are actually signs of over-replacement — too much thyroid hormone. These are the same symptoms as hyperthyroidism:

Racing or pounding heartbeat (palpitations)

Chest tightness or chest pain

Excessive sweating, especially at night

Nervousness, anxiety, or feeling jittery

Tremors (shaking hands)

Insomnia or difficulty sleeping

Increased appetite or unexplained weight loss

Diarrhea

If you experience these symptoms, contact your doctor. Do not stop taking your medication abruptly—a dose adjustment is usually what's needed.

Serious Side Effects: When to Seek Immediate Help

In rare cases, especially if the dose is significantly too high or in patients with underlying heart disease, Westhroid can cause serious cardiac effects:

Chest pain that is severe, squeezing, or radiating to the arm or jaw — call 911 immediately

Rapid irregular heartbeat (atrial fibrillation) — seek emergency care

Allergic reaction (rash, hives, swelling of face, lips, tongue, or throat) — call 911 or go to an ER. Note: true allergies to porcine thyroid are rare but possible, especially in patients with pork allergies

These serious effects are uncommon in patients taking Westhroid at an appropriate dose, but they represent important warning signs that require immediate medical attention.

Who Should Be Extra Cautious with Westhroid?

Certain patients need closer monitoring on Westhroid:

Patients with heart disease, angina, or arrhythmias — thyroid hormone increases cardiac demand; dose should be started low and titrated slowly

Elderly patients — more sensitive to thyroid hormone; risk of osteoporosis and atrial fibrillation with over-replacement

Patients with diabetes — thyroid hormone can affect blood glucose levels, requiring closer monitoring

Patients with adrenal insufficiency — thyroid hormone can unmask or worsen adrenal problems; adrenal status should be assessed before starting NDT

Pregnant patients — thyroid hormone requirements increase in pregnancy; more frequent monitoring is needed

Side Effects of Under-Treatment to Be Aware Of

It's also important to recognize signs that your Westhroid dose is too low—symptoms of hypothyroidism returning:

Fatigue, sluggishness, brain fog

Weight gain or difficulty losing weight

Hair loss or dry skin

Cold intolerance

Constipation, slow heart rate, depression

For information on medications that interact with Westhroid and may affect how well it works, see our Westhroid drug interactions guide.

If you're having trouble filling your Westhroid prescription, medfinder can help you locate a pharmacy near you that has it in stock.