What You Should Know About Cytomel Side Effects

Cytomel (Liothyronine Sodium) is a synthetic thyroid hormone used to treat hypothyroidism and certain thyroid conditions. Like all medications, it can cause side effects — some mild and temporary, others that need immediate medical attention.

This guide covers the most common side effects, the serious ones to watch for, and practical tips for managing them. If you're new to Cytomel, you may also want to read our overview of what Cytomel is and how it's used.

What Is Cytomel?

Cytomel contains Liothyronine, a synthetic form of the T3 thyroid hormone. T3 is the active form of thyroid hormone that your body uses to regulate metabolism, energy, and many other functions. Cytomel works faster and has a shorter duration than Levothyroxine (T4), which is why it requires careful dosing. For a deeper look at how Cytomel works in your body, see our mechanism of action guide.

Common Side Effects of Cytomel

Most common side effects of Cytomel are signs that your dose may be slightly too high. They often improve as your body adjusts or after a dose reduction. According to FDA labeling, common side effects include:

• Headache
• Irritability and nervousness
• Increased sweating
• Heat intolerance — feeling unusually warm
• Tremor — slight shaking, especially in the hands
• Diarrhea or increased bowel movements
• Nausea
• Menstrual changes — lighter or irregular periods
• Temporary hair loss — more common in children starting treatment

These side effects are generally mild and often resolve within the first few weeks of treatment. If they persist or bother you, let your doctor know — a dose adjustment may help.

Serious Side Effects: When to Call Your Doctor

Some side effects are more serious and may require immediate medical attention. Contact your doctor or go to the emergency room if you experience:

• Rapid or irregular heartbeat (pounding, racing, or skipping beats)
• Chest pain or tightness
• Shortness of breath
• Seizures
• Signs of adrenal crisis — severe weakness, dizziness, nausea, or fainting (especially if you have adrenal insufficiency)

Long-term use of Cytomel at doses that are too high can also lead to:

• Bone loss (osteoporosis) — particularly in postmenopausal women
• Heart problems — including heart failure and irregular heart rhythms

FDA Boxed Warning

Cytomel carries an FDA boxed warning: Thyroid hormones should not be used for weight loss. In patients with normal thyroid function, doses within the normal range won't cause weight loss. Higher doses can cause serious, life-threatening side effects — especially when combined with weight-loss drugs containing sympathomimetic amines.

Who's Most at Risk for Side Effects?

Certain groups need extra caution with Cytomel:

Older Adults

Elderly patients are more sensitive to thyroid hormones and should start at a lower dose (5 mcg per day). The risk of heart-related side effects — including arrhythmias, angina, and heart attack — is higher in this group.

People with Heart Disease

If you have a history of heart disease, coronary artery disease, or heart failure, Cytomel must be started at a very low dose and increased slowly. Your doctor should monitor you closely for cardiac symptoms.

People with Adrenal Insufficiency

If your adrenal glands don't produce enough cortisol, starting Cytomel without first correcting this can trigger an adrenal crisis. Your doctor should evaluate and treat adrenal insufficiency before prescribing Cytomel.

Pregnant or Breastfeeding Women

Cytomel is considered safe in pregnancy, but doses may need adjustment as pregnancy progresses. It does pass into breast milk, but is generally considered compatible with breastfeeding. Work closely with your doctor to monitor your thyroid levels during and after pregnancy.

Children

Children may experience temporary hair loss when starting Cytomel. Pediatric dosing starts at 5 mcg per day and is increased gradually under close medical supervision.

How to Manage Common Side Effects

Here are some practical tips for dealing with the most common Cytomel side effects:

Nervousness or Jitteriness

This usually means your dose is slightly too high. Don't adjust your dose on your own — call your doctor. In the meantime, reducing caffeine intake may help.

Sweating and Heat Intolerance

Stay hydrated, wear layered clothing, and let your doctor know if it's significantly affecting your daily life.

Headache

Over-the-counter pain relievers like acetaminophen are generally safe, but check with your doctor or pharmacist first. Headaches often improve as your body adjusts to the medication.

Diarrhea

Eat smaller, more frequent meals and stay hydrated. If diarrhea is severe or lasts more than a few days, contact your doctor.

Hair Loss

Temporary hair loss is usually a sign that your body is adjusting to the new hormone level. It typically resolves within a few months. If it continues, talk to your doctor about your dose.

Tremor

Slight hand tremor is common at the beginning of treatment. If it's interfering with daily activities, your dose may need to be reduced.

When to Call Your Doctor vs. When to Go to the ER

Call your doctor if you experience:

• Persistent headaches, nervousness, or diarrhea
• Menstrual changes
• Hair loss that doesn't improve
• Any side effect that bothers you or doesn't go away

Go to the ER if you experience:

• Chest pain or pressure
• Rapid or very irregular heartbeat
• Difficulty breathing
• Seizures
• Severe dizziness or fainting

Final Thoughts

Most people who take Cytomel tolerate it well, especially when the dose is carefully adjusted by their doctor. The key is to start low, go slow, and keep up with your follow-up lab work.

If you're experiencing side effects and thinking about alternative medications, talk to your doctor before making any changes. And if you need help finding Cytomel or its generic at a pharmacy near you, Medfinder can help you check stock availability.