Tirosint Side Effects: What You Need to Know

Starting a new medication always comes with questions — and Tirosint is no different. While most people tolerate it well, understanding the potential side effects helps you know what's normal, what's not, and when to contact your doctor.

This guide covers the common and serious side effects of Tirosint based on FDA labeling, plus tips for managing them.

What Is Tirosint?

Tirosint is a brand-name Levothyroxine Sodium gel capsule made by IBSA Pharma. It's used to treat hypothyroidism (underactive thyroid) and as an adjunct therapy for certain thyroid cancers. Unlike standard Levothyroxine tablets, Tirosint contains only three inactive ingredients — gelatin, glycerin, and water — which may reduce the risk of reactions to fillers and dyes found in tablets.

To understand how Tirosint works in your body, see our guide on Tirosint's mechanism of action.

Common Side Effects

The most common side effects of Tirosint are generally related to your body adjusting to the medication or receiving slightly too much thyroid hormone. They include:

• Hair loss — usually temporary during the first few months of treatment. Hair typically regrows once your body adjusts.
• Weight changes — you may notice mild weight loss as your metabolism normalizes, or weight fluctuations during dose adjustments.
• Appetite changes — increased or decreased appetite as thyroid levels stabilize.
• Headache — mild headaches may occur early in treatment.
• Menstrual irregularities — changes in period timing or flow may happen as thyroid levels are corrected.
• Heat sensitivity — feeling warmer than usual or being more sensitive to heat.
• Sweating — increased perspiration, especially if the dose is too high.

These side effects are usually mild and often improve as your doctor adjusts your dose to find the right level for you. Most patients on the correct dose of Tirosint experience few or no side effects.

Serious Side Effects

Serious side effects are less common but require immediate medical attention. Contact your doctor right away — or go to the emergency room — if you experience:

• Rapid or irregular heartbeat (tachycardia, palpitations, arrhythmias) — this may mean your dose is too high
• Chest pain or angina — especially concerning in patients with heart disease
• Shortness of breath — difficulty breathing could signal a cardiac issue
• Seizures — rare but possible, particularly with dose changes
• Signs of hyperthyroidism — excessive sweating, tremors, nervousness, insomnia, unexplained fever, or rapid weight loss
• Bone density loss — long-term overtreatment can weaken bones, particularly in postmenopausal women
• Heart failure symptoms — swelling in the legs, extreme fatigue, shortness of breath when lying down

Boxed Warning

Tirosint 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 help with weight loss. Larger doses can cause serious or life-threatening toxicity, especially when combined with weight-loss drugs containing sympathomimetic amines.

Side Effects in Specific Populations

Elderly Patients

Older adults, especially those with cardiovascular disease, are more sensitive to the effects of thyroid hormones. Doctors typically start elderly patients on a lower dose (12.5-25 mcg per day) and increase gradually. Rapid dose increases in this group can trigger heart problems.

Pregnant Patients

Thyroid hormone requirements often increase during pregnancy. Pregnant patients taking Tirosint should have their TSH monitored each trimester. Undertreating hypothyroidism during pregnancy can harm fetal development, so dose adjustments are common and expected.

Patients With Heart Conditions

If you have coronary artery disease, heart failure, or arrhythmias, your doctor will likely start you on a very low dose and titrate slowly. The risk of cardiac events is higher in this population.

Patients With Adrenal Insufficiency

If you have untreated adrenal insufficiency, starting thyroid hormone replacement can trigger an adrenal crisis. Your doctor must treat adrenal insufficiency with corticosteroids before starting Tirosint.

How to Manage Tirosint Side Effects

Here are practical tips for dealing with common side effects:

Take It Correctly

Many side effects stem from inconsistent absorption or incorrect dosing. For best results:

• Take Tirosint on an empty stomach, 30-60 minutes before breakfast
• Swallow the capsule whole
• Avoid calcium, iron, and antacids within 4 hours
• Take it at the same time every day

For a complete list of things to watch out for, see our guide on Tirosint drug interactions.

Keep Up With Lab Work

Your doctor will check your TSH levels regularly — typically every 6-8 weeks after a dose change, then every 6-12 months once stable. This is the best way to catch over- or under-dosing before side effects become a problem.

Track Your Symptoms

Keep a simple log of how you feel — energy levels, mood, weight, heart rate. This helps your doctor make better dosing decisions at your next visit.

Don't Adjust Your Dose on Your Own

Even small changes in Levothyroxine dose (as little as 12.5 mcg) can make a meaningful difference. Never increase, decrease, or stop your Tirosint without talking to your doctor first.

Report New Symptoms Promptly

If you develop new symptoms after starting Tirosint or after a dose change, call your doctor. It's better to report something minor than to ignore something serious.

Tirosint vs. Levothyroxine Tablet Side Effects

Because Tirosint contains only three inactive ingredients (gelatin, glycerin, and water), some patients who had side effects from Levothyroxine tablets — like stomach upset, headaches, or allergic reactions to dyes and fillers — report fewer issues with Tirosint. If you suspect your side effects are related to inactive ingredients in your current thyroid medication, talk to your doctor about whether switching to Tirosint might help.

Learn about alternatives to Tirosint if you're comparing options.

Final Thoughts

Most people who take Tirosint at the correct dose have few or no side effects. The key is working closely with your doctor to find the right dose, taking the medication consistently, and keeping up with lab work. If you experience any serious symptoms — especially chest pain, rapid heartbeat, or signs of hyperthyroidism — contact your doctor immediately.

If you're looking for Tirosint, Medfinder can help you find a pharmacy with it in stock near you.