Levothyroxine vs Mirtazapine: side-by-side comparison
Levothyroxine (Thyroid hormone replacement) and Mirtazapine (Atypical antidepressant (NaSSA)) belong to different therapeutic classes and are rarely substitutes for each other. The comparison is useful when a single patient is weighing both options for adjacent or overlapping needs.
| Property | Levothyroxine | Mirtazapine |
|---|---|---|
| Therapeutic class | Thyroid hormone replacement | Atypical antidepressant (NaSSA) |
| CAS | 51-48-9 | 85650-52-8 |
| ATC | H03AA01 | N06AX11 |
| Molecular weight | 776.87 g/mol | 265.36 g/mol |
| Brands with this active ingredient | 1 | 1 |
What they share
Levothyroxine and Mirtazapine share the common regulatory framework for prescription active ingredients, bioequivalence standards for generics, and pharmacist oversight. Beyond that, points in common are limited.
Key differences
Levothyroxine acts by a different mechanism than Mirtazapine, with indications that barely overlap. Comparing the two is useful when a clinician has mentioned both in the same context or the patient wants to understand why one was prescribed instead of the other.
Mechanisms compared
Levothyroxine: Levothyroxine replaces deficient endogenous thyroxine, which is converted in tissues to the active hormone triiodothyronine (T3) by deiodinase enzymes. Mirtazapine: Mirtazapine antagonises presynaptic α2-adrenergic autoreceptors and heteroreceptors, increasing noradrenaline and serotonin release.
Indications compared
Levothyroxine: Levothyroxine is approved for hypothyroidism of any cause (Hashimoto thyroiditis, post-thyroidectomy, post-radioiodine, congenital), goitre and TSH suppression after differentiated thyroid cancer. Mirtazapine: Mirtazapine is approved for major depressive disorder.
Safety profile
Levothyroxine: At correct dose, levothyroxine has minimal adverse effects because it replaces a hormone the body normally produces. Mirtazapine: Common adverse effects include sedation (highest at low doses 7.5–15mg, paradoxically less at higher doses), increased appetite, weight gain, dry mouth and dizziness.
Frequently asked questions
Is Levothyroxine better than Mirtazapine? ▾
Levothyroxine and Mirtazapine are not "better or worse" — they treat different things. The sensible question is which fits your specific need.
Can Levothyroxine and Mirtazapine be combined? ▾
Whether they can be combined depends on the indications and the interaction profile of each. If both are in a single prescription, the prescriber has weighed it; in self-medication they should never be combined.
Do they have the same side-effect profile? ▾
No — they belong to different classes and have distinct side-effect profiles. Each has its own prescribing information.
Products with Levothyroxine
Products with Mirtazapine
The information on this website is provided for reference and educational purposes only. It does not replace consultation with a qualified healthcare professional.