Levothyroxine 300mcg
Generic For: Synthroid
Levothyroxine 300mcg (brand name Synthroid) is a synthetic thyroid hormone used to treat hypothyroidism and certain types of goiter. It replaces the hormone your thyroid gland normally produces to help restore normal metabolism and energy levels. After a licensed provider reviews your prescription, your medication ships from a licensed U.S. pharmacy.
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90-day supply · $0.28/tablet
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A thyroid hormone replacement for hypothyroidism, goiter, and thyroid hormone deficiency
Levothyroxine 300mcg Quick Facts
| Drug class | Thyroid hormone replacement |
|---|---|
| Treats | Hypothyroidism, goiter, TSH suppression in thyroid cancer |
| Form | Tablet |
| Typical dosing | Take 1 tablet by mouth daily in the morning. |
| Prescription required | Yes — prescription only |
What Is Levothyroxine 300mcg?
Levothyroxine is a synthetic (man-made) version of thyroxine (T4), the main hormone produced by the thyroid gland. When the thyroid does not make enough hormone — a condition called hypothyroidism — levothyroxine replaces it to support normal metabolism, heart function, and energy. The 300mcg strength is a higher-dose tablet typically prescribed for patients who require substantial hormone replacement, as determined by lab testing. It is taken once daily and usually requires ongoing use with periodic blood tests to keep levels in range.
What Does Levothyroxine 300mcg Treat?
Primary hypothyroidism
Secondary (pituitary) hypothyroidism
Tertiary (hypothalamic) hypothyroidism
Congenital hypothyroidism
Pituitary TSH suppression in well-differentiated thyroid cancer
Euthyroid goiter management (select cases)
Levothyroxine 300mcg Dosage
Adults: approximately 1.6 mcg/kg by mouth once daily.
Take on an empty stomach, 30–60 minutes before breakfast.
Dose individualized based on TSH labs; continue as directed long term.
Your prescriber will determine the dose and duration that are right for you. Always follow the directions on your prescription label.
Levothyroxine 300mcg Side Effects
Common side effects
- Hair thinning (temporary, early in treatment)
- Headache
- Insomnia
- Nervousness or irritability
- Increased appetite
- Sweating
- Mild weight loss
- Diarrhea
Serious side effects
Stop taking this medication and seek medical attention right away if you experience:
- Chest pain or irregular heartbeat
- Rapid or pounding heart rate
- Shortness of breath
- Signs of allergic reaction (rash, swelling, trouble breathing)
- Severe tremor or heat intolerance
- Seizures (rare)
Warnings & Interactions
Not for weight loss; large doses may cause serious or life-threatening effects
Do not use with uncorrected adrenal insufficiency
Use caution with heart disease; may worsen angina or arrhythmias
May affect blood sugar control in diabetes; monitor glucose
Increases effect of warfarin; INR monitoring needed
Separate from calcium, iron, and antacids by at least 4 hours
Long-term over-replacement may decrease bone mineral density
Tell your prescriber about all medications, supplements, and health conditions before starting levothyroxine 300mcg.
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