Plan B vs Allegra: side-by-side comparison
Plan B (Hormones and Birth Control) and Allegra (Allergy and Antihistamines) belong to different therapeutic classes and are rarely interchangeable. This page compares the medications' purposes, mechanisms and the situations where each is used.
| Property | Plan B | Allegra |
|---|---|---|
| Active ingredient | Levonorgestrel | Fexofenadine |
| Manufacturer | Foundation Consumer Healthcare | Sanofi |
| Class | Hormones and Birth Control | Allergy and Antihistamines |
| Strengths | 1.5mg | 30mg, 60mg, 120mg, 180mg |
| Forms | tablet | tablet, oral suspension, orodispersible tablet |
What's the same
Plan B and Allegra 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
Plan B belongs to Hormones and Birth Control while Allegra belongs to Allergy and Antihistamines. 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
Plan B: Plan B's primary mechanism is delaying or preventing ovulation when taken before the LH surge. Allegra: Fexofenadine selectively blocks peripheral H1 histamine receptors, antagonising the effects of histamine on vasodilation, capillary permeability, sensory nerve endings and smooth muscle.
When Plan B is preferred
Plan B is indicated for emergency contraception after unprotected intercourse or known/suspected contraceptive failure, in women of reproductive age.
When Allegra is preferred
Allegra is approved in adults and children for the treatment of seasonal allergic rhinitis and chronic idiopathic urticaria.
Frequently asked questions
Is Plan B or Allegra better? ▾
Plan B and Allegra 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 Plan B to Allegra? ▾
Switching between Plan B and Allegra 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 Plan B and Allegra 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 Plan B comparisons
The information on this website is provided for reference and educational purposes only. It does not replace consultation with a qualified healthcare professional.