Efficacy of generics versus brand name drugs

Efficacy of generics versus brand name drugs is a bit more complicated than both of you let on.
To elaborate:
1. Yes, the active ingredient(s) is(are) chemically identical between brand name and generic drugs. We will assume that the manufacturer of the generic drug has done its job and synthesized the ingredients correctly, as well as established the correct purities and dosages.

2. The placebo effect is real, and the *perceived* stature of a brand-name drug may contribute to its greater efficacy in a given patient. That, of course, is not to say that the generic drug is actually less biologically active, but we cannot ignore non-pharmacological effects.

3. The delivery system CAN make a difference. For example, some drugs have a time-release formulation, or have other ingredients that may modify its bioavailability. These features of a drug are not necessarily captured in the chemical patent--and when a generic form is made, it is possible that differences in delivery system may have an impact on overall efficacy.

4. That said, a generic version is extremely, EXTREMELY unlikely to be ineffective compared to its brand-name version if the latter is found effective. If that were the case even for a small percentage of patients taking the drug, that would have very obvious and enormous consequences.

The active ingredient(s) in a generic medication MUST be identical to the brand and the pharmacokinetic characteristics MUST be comparable. Having said that it's not uncommon to see slight differences between a brand medication and its generics.

1. The brand name manufacturers have to go through some rigorous processes in order to gain FDA's approval. By rigorous processes, I mean conducting 3 mandatory sometimes large-scale RCTs to substantiate the drug's safety and efficacy. Compare this to a generic drug where these requirement are sometimes unnecessary.

2. The pharmacokinetics have to be comparable. This means that the generic pharmacokinetics characteristics have to be good enough to pass the threshold set by the FDA in order to be approved. And in most cases they are.

3. Individual variability is also a big factor to why most people respond differently to medications. Differences in genetic components, enzymes and drug interactions are sometimes excluded from these discussions.

4. Inactive ingredients like fillers used might also contribute to this slight differences. This could be in the form of slowing down the absorption rate,etc
From my experience, close 95-98% respond to generic but there's still 3-5% that don't.