Some drugs do well in generic production. Others do not. The posted experiences of people with Coumadin and generic warfarins over the years seem to show that there is a genuine equivalence. If I were using warfarin, I'd not hesitate to go with the generic, based on what I've seen here.
However, not all generic drugs work as well as their counterparts. Ross brought out this from Barr Labs, a large generics manufacturer, and it's quite true, as far as it goes:
In order to be deemed therapeutically equivalent to brand products, generic drugs must have the same active ingredients, same dosage form, same standards for purity and quality, same standards for manufacturing, and same amount of drug absorbed over the same time as the equivalent brand product. Generics are also required to meet the same stringent government standards for strength, purity and potency as the brand version.
Manufacturers of generics are not required to run their finished products through the same stringent efficacy testing required to bring original drugs into the marketplace. Their requirements are that the components and manufacturing process be pure and that a certain amount of active ingredient per pill be absorbable by the patient. As such, the patients can be exposed to untested variations in delivery strength over time or variations in efficacy of the delivered product due to altered chemical availability of the compound in the body due to binders or other generally innocuous ingredients in the pills.
In some blood pressure medications, antidepressents, and similar drugs, the other filllers and binding agents in the tablets are different from the originals, and may cause uneven levels of the active ingredient over the dosage period. The same amount of medication gets into your system over twelve hours, but 65% of it may pass through during the first four hours, and only a tiny percentage by the tenth and eleventh hours. Or it might peak at six hours.
The results of this are uneven, as people are all different. Many people notice no difference, and the product is a success for them and saves them money. Others may experience a sudden change in side effects, based on the heavier drug burden during certain hours of the cycle. You may have experienced this at some point yourself, when a drugstore you use switches manufacturers, or when you switch drugstores.
I've experienced it with different generic manufacturers of Atenolol from different drugstores. One store's generic brand is fine. The other causes paresthesia (tingling in hands and feet), sweating, and dry eye.
One example of a generic oops was birth control 28-pill full-cycle packs that each contained seven hormone birth control pills and 21 placebos. Some generic manufacturers have had suspensions of license for improper testing or manufacture, such as Able Labs, who manufactured a range of generic drugs from acetominophen to generic tramadol, and had to recall them all.
I'm not trying to state that generic drugs are often unreliable or that they will work differently than the original product. It should be noted that some generics are actually manufactured by the original manufacturer, or licensed and monitored by them (and that original manufacturers can run afoul of production issues as well). However, I am saying that the more intricate the drug's nature, the greater the possibility of differences. If you notice a change in your reaction from a new batch of your prescription, you should determine if the change is enough to be a problem for you, and not just live with it.
Best wishes,
