Levothyroxine (Synthroid Generic) – Complete Product Information

What is Levothyroxine?

Levothyroxine is a synthetic form of the thyroid hormone thyroxine (T4). It is used to treat hypothyroidism, a condition in which the thyroid gland does not produce enough thyroid hormone. It may also be used to treat or prevent goiter and certain thyroid cancers. Common brand names include Synthroid, Levoxyl, and Tirosint.

Levothyroxine helps restore normal hormone levels, improving energy, metabolism, and overall well-being. It is one of the most commonly prescribed medications in the United States.

What is Levothyroxine Used For?

According to the FDA, levothyroxine is approved to treat:

• ✔️ Hypothyroidism – underactive thyroid, including Hashimoto's thyroiditis.
• ✔️ Thyroid-stimulating hormone (TSH) suppression – in certain thyroid cancer patients.
• ✔️ Goiter – prevention and treatment in selected patients.

Doctors may also prescribe it for other thyroid-related conditions. Always follow your prescriber's instructions.

Available Dosages and Forms

Levothyroxine is available as oral tablets in many strengths, measured in micrograms (mcg):

• Tablets: 25 mcg, 50 mcg, 75 mcg, 88 mcg, 100 mcg, 112 mcg, 125 mcg, 137 mcg, 150 mcg, 175 mcg, 200 mcg, 300 mcg
• Capsules (Tirosint): 13 mcg, 25 mcg, 50 mcg, 75 mcg, 88 mcg, 100 mcg, 112 mcg, 125 mcg, 137 mcg, 150 mcg

Generic levothyroxine is available in the same strengths and is usually less expensive.

Brand Synthroid vs Generic Levothyroxine

Both contain the same active ingredient and must meet FDA standards for quality and potency. However, some patients may notice differences when switching between brand and generic due to inactive ingredients or manufacturing variations. Many people do well on generics, but it is important to stay on a consistent formulation. If your pharmacy changes your generic supplier, your doctor may want to recheck your thyroid levels.

How to Take Levothyroxine Safely

Always follow your healthcare provider's instructions. Levothyroxine is usually taken once daily in the morning on an empty stomach, at least 30–60 minutes before breakfast.

1. Take levothyroxine with a full glass of water.
2. Wait at least 30–60 minutes before eating or drinking coffee.
3. Take it at the same time each day to keep hormone levels stable.
4. Do not stop taking it without consulting your doctor, even if you feel well.
5. Regular blood tests are needed to monitor your thyroid levels.

Common Side Effects and Precautions

Like all medications, levothyroxine may cause side effects, especially if the dose is too high. The most common include:

• Increased appetite
• Weight loss
• Nervousness or anxiety
• Difficulty sleeping
• Heat intolerance
• Increased sweating
• Headache
• Palpitations

Serious side effects requiring immediate medical attention include chest pain, rapid or irregular heartbeat, severe dizziness, and signs of an allergic reaction. This is not a complete list. Read the full FDA label or consult your pharmacist.

Important: Levothyroxine may interact with certain antacids, iron supplements, calcium supplements, and some medications. Take levothyroxine at least 4 hours apart from these products. Tell your doctor about all medications and supplements you take.

📚 Medical Sources We Rely On

All product information is based on official FDA labeling (FDA Levothyroxine Approval) and peer-reviewed research available on PubMed. Our content is reviewed by a licensed pharmacist. See our About page for credentials.