A patient often wonders why insurance companies choose a generic alternate to a prescription over a brand name drug.
The one and only reason is that brand name drugs are around 80 to 85% more expensive than generic counter parts. The effectiveness of the drug (efficacy) is usually the same between generic and brand.
A few patients find the body absorption rates are better for brand than generics. This is not statistically significant.
It may not be advisable for you to get a generic version of narrow therapeutic index drugs, in which tiny differences in the dose or formulation may cause a reaction (examples include blood thinners, lithium, and thyroid injections). These types of drugs (aminoglycosides, ciclosporin, carbamazepine, digoxin, digitoxin, flecainide, lithium, phenytoin, phenobarbital, rifampicin, theophylline, warfarin) are sensitive to dose and/or formulation and often cause Drug Related Problems. Brand name drugs are preferred for these types of prescriptions. Warfarin and Jantoven are blood thinners and are generic version of brand name Coumadin and are ten times cheaper. Keep your physician informed of any abnormal effects when you are prescribed narrow therapeutic index drugs.
Source: Open literature