WASHINGTON—Take the generic drug clonidine for high blood pressure? Double-check that you didn’t leave the drugstore with Klonopin for seizures, or the gout medicine colchicine.

Mixing up drug names because they look or sound alike—like this trio—is among the most common types of medical mistakes, and it can be deadly. Now new efforts are aiming to stem the confusion, and make patients more aware of the risk.

Nearly 1,500 commonly used drugs have names so similar to at least one other medication that they’ve already caused mix-ups, says a major study by the U.S. Pharmacopeia, which helps set drug standards and promote patient safety. Last week the influential group opened a Web-based tool to let consumers and doctors easily check if they’re using or prescribing any of these error-prone drugs, and what they might confuse it with. Try to spell or pronounce a few on the site —www.usp.org—and it’s easy to see how mistakes can happen. Did you mean the painkiller Celebrex or the antidepressant Celexa?

Due out later this fall is a more patient-oriented Web site, a partnership of the nonprofit Institute for Safe Medication Practices and online health service iGuard.org, that will send users e-mail alerts about drug-name confusion. And the Food and Drug Administration—which currently rejects more than a third of proposed names for new drugs because they’re too similar to old ones—is preparing a pilot program that would shift more responsibility to manufacturers to guard against name confusion. The goal is to spell out how to better test for potential mix-ups before companies seek approval to sell their products.