Eli5: what is the difference between a generic drug to the original drug, and why do some doctors will swear by the original drug?

Question

Eli5: what is the difference between a generic drug to the original drug, and why do some doctors will swear by the original drug?

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Answer 1

A drug is made up of active ingredients and inactive ones. A pill might have a tiny amount of the actual drug and the rest is various other ingredients – some of them are designed to ensure that the actual drug is released in the right part of the body to get where it needs to go to be effective – the pH of the stomach is different than the intestines for example. The rest of the pill may include various fillers or dyes.

A company doesn’t have to do their own clinical studies in humans and animals to get a generic drug approved, you only have to show that the active ingredient is the same and that the generic drug is bioequivalent to the original drug (meaning that the active ingredient is the same and will release the same way in the body). The inactive ingredients can be different and the manufacturing methods can be different.

Companies aren’t allowed to make a generic drug unless the patents on the original drug have expired. Once the patents expire, any company that wants can apply to make a generic, and if it’s a big drug you can easily have 5-10 companies all making generics. (There are a lot of complex FDA rules on this but that’s beyond the scope of ELI5.)

Normally, the generic version is much cheaper than the original drug, so almost everyone will want the generic once it becomes available. If a doctor just writes a prescription and doesn’t say specifically that it has to be the original drug, a pharmacy will usually (and in many states is required to) give you the generic even if you don’t ask for it.

There are rare cases where doctors will insist on the patient getting the original drug – (1) a patient has a lot of allergies, the patient can take the original drug without a problem, and the doctor is worried about the patient being allergic to the inactive ingredients in the generic, (2) an elderly patient who knows what pills to take when by color and shape, and the doctor doesn’t want to confuse them by changing their routine, or (3) for whatever reason the doctor doesn’t trust a particular generic manufacturer or generic version of a drug to be genuinely safe and identical – “that company has had a lot of problems; I wouldn’t use anything they make.”