Synthroid vs Plan B: side-by-side comparison
Synthroid (Levothyroxine) and Plan B (Levonorgestrel) both belong to the Hormones et contraception class. They share clinical context but use different active ingredients. The choice between them depends on mechanism nuances, side-effect profile and individual response.
| Property | Synthroid | Plan B |
|---|---|---|
| Active ingredient | Levothyroxine | Levonorgestrel |
| Manufacturer | AbbVie | Foundation Consumer Healthcare |
| Class | Hormones et contraception | Hormones et contraception |
| Strengths | 25mcg, 50mcg, 75mcg, 100mcg, 150mcg | 1.5mg |
| Forms | tablet | tablet |
What's the same
Synthroid and Plan B both belong to the Hormones et contraception class and are used for partially overlapping indications. The active ingredients — Levothyroxine vs Levonorgestrel — share the same therapeutic approach, so many safety and management points carry across both.
Key differences
Meaningful differences are in active ingredient (Levothyroxine vs Levonorgestrel), strengths (25mcg, 50mcg, 75mcg, 100mcg, 150mcg vs 1.5mg), forms (tablet vs tablet), and the mechanism, half-life and side-effect nuances that distinguish members of the class.
Mechanism and action
Synthroid: La lévothyroxine remplace la thyroxine endogène déficitaire, convertie dans les tissus en hormone active, la triiodothyronine (T3), par les enzymes désiodases. Plan B: Le mécanisme principal de Plan B est le retard ou le blocage de l'ovulation lorsqu'il est pris avant le pic de LH.
When Synthroid is preferred
Synthroid est autorisé dans l'hypothyroïdie de toute cause (thyroïdite de Hashimoto, post-thyroïdectomie, post-iode radioactif, congénitale), dans le goitre et dans la freination de la TSH après cancer thyroïdien différencié.
When Plan B is preferred
Plan B est indiqué en contraception d'urgence après un rapport non protégé ou un échec de contraception avéré ou suspecté, chez la femme en âge de procréer.
Questions fréquentes
Is Synthroid or Plan B better? ▾
There is no single answer. Synthroid and Plan B both belong to the Hormones et contraception class but differ in mechanism nuances, half-life and side-effect profile. Preference depends on the patient, the prescriber and prior response to other therapies.
Can I switch from Synthroid to Plan B? ▾
Switching within the Hormones et contraception class is done under supervision, typically using equivalent doses and a follow-up period to confirm response and tolerance. It is not a self-directed decision.
Do Synthroid and Plan B have the same side effects? ▾
They share many of the Hormones et contraception class side effects, with differences from mechanism and dose. Each medication's prescribing information lists specifics.
More Synthroid comparisons
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