If you need to fill a prescription or pick up an over-the-counter medication from the drugstore, you may wonder if you’ll save money with a generic, and if it will work as well. Here's what you need to know.

What Is a Generic Drug?

A generic drug has the same active ingredients and strength as a brand-name drug. It also works the same way. But a generic drug may have different inactive ingredients -- things like fillers, colorings, and flavorings. Because of these slight differences, your body might absorb a little more or a little less of a generic drug (about 3.5% more or less, according to studies) than the brand-name version. The FDA says that this is “expected and acceptable" and shouldn't affect the generic's performance.

Pharmacists know this. That's why, when surveyed, 91% of them said they buy generic, store-brand headache remedies instead of brand-name ones.

Nine out of 10 prescriptions written in the United States are for generic drugs. In fact, many pharmacies will automatically give you the generic unless your doctor writes "do not substitute" or "dispense as written" on the prescription.

Why Are Generic Drugs Cheaper?

Drug companies spend a lot on research, development, and marketing when they create a drug. They apply for a patent to block competitors so that they can make up some of these costs. By the time a drug hits the market, the patent usually protects it for about 12 years. The FDA also grants periods of exclusivity to new drugs -- usually 5 to 7 years. During this time, they're shielded from generic drug competition.

Generic drug makers don't have to fund animal and human trials the way that a company does when it introduces a new medication. Plus, once generic drugs get the green light, several manufacturers usually start making them, which drives down costs further. For these reasons, generic drugs are about 85% cheaper than brand-name ones.

What About ‘Therapeutic Alternative’ Drugs?

Sometimes, when a generic is not yet available for a brand-name drug, a doctor will consider prescribing a different, less expensive medication that has a similar effect. This is known as "therapeutic interchange" or "therapeutic substitution.” The replacement drug is called a "therapeutic alternative." You and your doctor might discuss this and decide it's the best course of action.

But sometimes, therapeutic substitution can happen without your knowledge, especially if you're in the hospital. Some major health organizations, like the American Psychiatric Association and the American Heart Association, oppose therapeutic substitution if nobody checks with the doctor who wrote the original prescription. They worry that swapping medications like antidepressants and statins could be dangerous, especially if someone doesn’t keep a close eye on the person who takes the medication.

What Questions Should I Ask My Doctor About Generic Drugs?

Your doctor may not prescribe you a generic at first. They may not realize that you're looking to save money. Or they may go ahead and prescribe a brand-name because they know it has worked well for other people like you. So be sure to ask if there's a generic option available. Some drugs have more than one.

You'll also want to discuss the safety of a generic if you'll be taking an NTI (narrow therapeutic index) drug. These are drugs in which small differences in dosages can cause serious reactions. The FDA doesn't keep an official list, but most experts agree that, for example, the blood thinner warfarin and the heart medication digoxin are NTI drugs.  

Because your body can absorb generics at a slightly different rate than the brand-name equivalent, your doctor may suggest you take a brand-name NTI drug, or may decide to watch you more closely while you're on the generic.

WebMD Medical Reference

From WebMD

More on Lowering the Cost of Medication