New or brand name drugs are protected in the United States by patent for 20 years. After the patent expires other companies can market the drug. These generic drugs may be identical chemically, and they may or may not be equivalent therapeutically to the original drug. They will have different binders, fillers, and dyes. Sometimes when a brand goes off patent the company may withdraw the original drug from the marketplace and begin making the same drug in a different form. They may produce a tablet instead of a capsule. Tablets and capsules have different bioavailability to the body and many times one cannot be substituted for the other. The body may not absorb the drug/generic as well or a rapidly.
Many generic drugs are just as effective as the proprietary (brand name) drug. Biochemical individuality of the patient can cause a wide variance in drug processing by the body. Doctors write prescriptions for the generic drugs because they are generally cheaper. Some insurance companies will not pay for a brand name or proprietary drug if a generic is available. In these cases the doctor must specify that the proprietary drug is a medical necessity, which is written as “dispense as written” on the prescription.
The FDA rates generics as A – an exact equivalent or B-if the bioavailability profile is different. Pharmacists are usually the only ones who know the rating for a generic. When switching from a brand drug to a generic, some patients may be able to tell a difference. In most cases the body will adjust to a generic drug with ease. For serious diseases a patient may want to check with the doctor or pharmacist before switching to a generic.