Synthroid vs Aygestin: side-by-side comparison
Synthroid (Hormones and Birth Control) and Aygestin (Women's Sexual Health) belong to different therapeutic classes and are rarely interchangeable. This page compares the medications' purposes, mechanisms and the situations where each is used.
| Property | Synthroid | Aygestin |
|---|---|---|
| Active ingredient | Levothyroxine | Norethindrone |
| Manufacturer | AbbVie | Various generics |
| Class | Hormones and Birth Control | Women's Sexual Health |
| Strengths | 25mcg, 50mcg, 75mcg, 100mcg, 150mcg | 5mg |
| Forms | tablet | tablet |
What's the same
Synthroid and Aygestin are used in very different patients, and the points in common are limited. The main shared element is that both meet regulatory standards for efficacy and safety and benefit from pharmacist oversight.
Key differences
Synthroid belongs to Hormones and Birth Control while Aygestin belongs to Women's Sexual Health. Indications, mechanisms and target populations differ. The comparison is most useful when a clinician has mentioned both medications and the patient wants to understand where each fits.
Mechanism and action
Synthroid: Levothyroxine replaces deficient endogenous thyroxine, which is converted in tissues to the active hormone triiodothyronine (T3) by deiodinase enzymes. Aygestin: Norethindrone binds to progesterone receptors and exerts progestational effects: thickening cervical mucus, suppressing the LH surge, thinning the endometrium and reducing endometrial implant activity in endometriosis.
When Synthroid is preferred
Synthroid is approved for hypothyroidism of any cause (Hashimoto thyroiditis, post-thyroidectomy, post-radioiodine, congenital), goitre and TSH suppression after differentiated thyroid cancer.
When Aygestin is preferred
Aygestin is approved for endometriosis-associated pain, abnormal uterine bleeding due to hormonal imbalance, and secondary amenorrhoea.
Frequently asked questions
Is Synthroid or Aygestin better? ▾
Synthroid and Aygestin are not interchangeable — they treat different conditions. Asking which is "better" is meaningful only when a clinician has weighed both for the same specific clinical scenario.
Can I switch from Synthroid to Aygestin? ▾
Switching between Synthroid and Aygestin is rarely an appropriate decision since they belong to different classes and treat different conditions. The real question is usually whether the diagnosis calls for one medication or the other — which the prescriber resolves.
Do Synthroid and Aygestin have the same side effects? ▾
No — they belong to different classes and have distinct side-effect profiles. Each medication has its own prescribing information.
More Synthroid comparisons
The information on this website is provided for reference and educational purposes only. It does not replace consultation with a qualified healthcare professional.