SynthroidvsLevothyroxine
Both are thyroid hormone • Side-by-side comparison
Synthroid vs Levothyroxine: Overview
Synthroid and levothyroxine are both thyroid hormone replacement medications used to treat hypothyroidism (underactive thyroid) and thyroid cancer. They contain the same active ingredient — synthetic T4 (thyroxine) — but Synthroid is the brand-name version manufactured by AbbVie, while levothyroxine is the generic. This makes Synthroid one of the relatively rare cases where a brand-name drug and its generic contain literally identical active ingredients, yet some patients and physicians have historically reported differences in clinical outcomes. The FDA considers all levothyroxine products bioequivalent, though slight variations in inactive ingredients between manufacturers can sometimes affect absorption. Consistency of brand or manufacturer is considered important for stable thyroid hormone levels.
Key Facts at a Glance
- ✓Same active ingredient (synthetic T4/thyroxine) — brand vs generic
- ✓The FDA considers them bioequivalent, but inactive ingredients differ between manufacturers
- ✓Synthroid costs significantly more than generic levothyroxine
- ✓Thyroid specialists often recommend staying consistent with one brand/manufacturer
- ✓Taken on an empty stomach, 30-60 minutes before breakfast for best absorption
- ✓Dosing requires regular TSH blood tests to ensure optimal levels
Synthroid
Drug AUsed For
- ✓ Hypothyroidism
Levothyroxine
Drug BUsed For
- ✓ Hypothyroidism
Key Differences
Which Should You Choose?
For most patients, generic levothyroxine works just as well as Synthroid and costs significantly less. The key is consistency — if you start on Synthroid, stay on it; if you start on generic, stay with the same manufacturer. Switching between products can cause fluctuations in TSH levels. If your thyroid levels are well-controlled on generic levothyroxine, there is typically no need to switch to the more expensive brand-name Synthroid. Your endocrinologist can advise based on your specific response to treatment.