Consumer Reports has no financial relationship with any advertisers on this site.

If you’ve ever had a cold that keeps you up at night coughing or painful urinary tract infections that recur regularly, you may have been tempted to simply help yourself to the antibiotics you’ve been storing since last year in your medicine cabinet. Or you might ask a friend or family member for a few pills.

But doctors don’t recommend taking the drugs without a current prescription, because numerous studies over the years have found that using antibiotics improperly can be risky.

Now, a new review of 31 previous studies, published in July in the Annals of Internal Medicine, suggests that such antibiotic misuse may be common among some people.

How common? The numbers ranged from as low as 1 percent in a primary care clinic to 66 percent among migrant workers, says lead study author Larissa Grigoryan, assistant professor of family and community medicine at Baylor College of Medicine in Houston.

This news is concerning, says Vance Fowler, an infectious disease specialist at Duke University Hospital in Durham, N.C., who was not part of the study.

“Many people don’t need these drugs,” he says. “By taking them, they raise their risk of experiencing side effects — some of them dangerous — and developing antibiotic resistance.” (Antibiotic resistance can make some bacteria less likely to respond to medications and some infections much harder to cure.)

Here’s what you need to know about this research and how to use antibiotics safely.

What the study found

To find out how common the use of antibiotics without a prescription is in the United States, researchers reviewed studies done in a wide variety of settings and populations.

These included the waiting rooms of urgent care centers and emergency rooms, clinics for treating sexually transmitted diseases, phone surveys and even a county jail.

Eventually, the researchers zeroed in on 31 studies. “One of the most common scenarios was people using leftover prescriptions, or borrowing from a friend or family member,” says Barbara Trautner, professor and director of Clinical and Health Services Research at Baylor and another of the study authors.

For instance, a 2018 Internet survey of 496 parents found that of the almost half who kept their child’s leftover antibiotics, 73 percent then gave them to a sibling or an unrelated child or adult.

In another study, a quarter of the patients in primary care clinics reported that they intended to use antibiotics without a prescription.

In addition, “In certain Hispanic or Latino neighborhoods, there’s easy access to antibiotics through flea markets and bodegas, or they’re able to get antibiotics from a relative who got them from another country, where they’re sold over the counter,” Trautner says.

Why weren’t people simply going to their doctors to seek prescriptions? Lack of health insurance, cost of physician visits, worries about missing work and embarrassment about being treated for sexually transmitted diseases were among the more frequent reasons reported.

“They’re trying to deal with health problems that require quick solutions, and for whatever reason they don’t have the ability to get to a physician,” Trautner says.

The risks of misuse

There are a number of reasons to avoid this do-it-yourself use of antibiotics. Effectiveness — or the lack thereof — is one. “We found that people often took antibiotics to treat viral colds, which won’t help you,” Trautner says. Antibiotics are useful only for bacterial infections.

And if you do have a bacterial infection, the antibiotics you have at home may be the wrong kind or dose for your condition. Even if it’s the right antibiotic and dose, you may not be getting enough of the pills to adequately treat your infection.

In addition, some antibiotics can have serious side effects. Clindamycin, for example, raises the risk of a C. difficile infection by destroying the good gut bacteria that keeps harmful ones at bay.

Certain other antibiotics, like tetracycline, could cause kidney damage if they’re taken after they’ve expired. Antibiotics can also interact with other prescription or over-the-counter products you’re taking, including supplements. Without your health-care professional’s oversight, you won’t know.

Finally, if you’re buying antibiotics online or “under the counter” at, say, a local flea market, you can’t be sure what you’re getting.

Then there’s the increasing threat of antibiotic resistance, which can render the drugs useless when they’re really needed. “I feel a real white-knuckle fear when I prescribe antibiotics, even for routine things like a urinary tract infection, because I don’t know if they’re going to work,” Trautner says. “We’re seeing more and more drug-resistant strains of bacteria out there.”

3 steps for safe use

• Don’t share or take leftover antibiotics. Throw away any old ones you have in your medicine cabinet.

• See your doctor if you think you have an infection that may be bacterial. Your health-care provider can do a thorough checkup and prescribe the appropriate medications.

• Don’t take these drugs if you don’t need them. “If your doctor just says you have a cold, don’t push for an antibiotic,” says William Schaffner, an infectious disease specialist at Vanderbilt University School of Medicine in Nashville. In addition to colds, many common illnesses — such as sore throats, sinus infections and pinkeye — are caused by viruses and clear up on their own.

 Copyright 2019, Consumer Reports Inc.

Consumer Reports is an independent, nonprofit organization that works side by side with consumers to create a fairer, safer, and healthier world. CR does not endorse products or services, and does not accept advertising. Read more at ConsumerReports.org.