Men trying to hold on to their hair often turn to Propecia to help them fight male pattern balding. The brand-name drug’s active ingredient is finasteride, which is also available as a generic alternative to Propecia.
The drug works by inhibiting a substance called 5-alpha reductase, which is an enzyme that changes testosterone into dihydrotestosterone (DHT). By reducing the amount of testosterone converted into DHT, the drug can slow, stop, or even reverse hair loss.
How Propecia and Finasteride Are Alike
Finasteride may be formulated with different inactive ingredients and sold as a generic, whereas Propecia is Merck’s specific formulation of finasteride with its own binding and inactive ingredients.
Propecia contains 1 mg of finasteride. Theoretically, a person can switch from taking 1-mg Propecia to 1-mg generic finasteride and get the same results. However, a small number of patients notice a difference in their symptoms when they switch from a name brand drug to a generic or when they switch from one generic finasteride drug to another.
How Propecia and Finasteride Differ
A generic tablet with 1 mg of finasteride differs from brand name Propecia by the use of different inactive or binding ingredients that are used to form each tablet. While these differences are usually negligible to the patient, there are some cases where a patient will break down the inactive ingredients in a generic differently than the inactive ingredients in a name brand drug, and this could affect how well it works.
Generic Drugs and Bioequivalence
The FDA sets stringent standards for generic drug manufacturers that want to offer alternatives to name brand drugs.
When approving generic drugs, the FDA demands adherence to several criteria:
- The active ingredient must be approved as safe and effective
- The generic must contain identical amounts of the same active ingredient in the same dosage form and method of administration
- The generic must meet standards for strength, quality, purity, and identity
- The generic must be bioequivalent to the name brand
To test for bioequivalence, generic manufacturers test the drugs on healthy volunteers and compare blood levels of the drug over time to blood levels of the name brand drug over the same period of time. To be considered bioequivalent, the generic must reach a blood serum level of 80% to 125% of what the name brand product achieves. In reality, the blood serum levels of generics are usually much closer than this, within about 3.5% of the blood serum levels of the name brand.