What Happens If You Take an Antibiotic You Don’t Need?

You’re not feeling well, but you can’t put your finger on why. You’ve heard the flu is going around, and your neighbor just had strep throat. It could be a bad cold or a sinus infection. Whatever it is, you’re ready for your symptoms to be over, and so you decide to ask your doctor for a prescription of antibiotics.

The problem is that depending on the cause of the illness, antibiotics may not work at all.

“When people are miserable and naturally want to feel better quickly, they often think antibiotics will help, but if you have a virus, antibiotics won’t do anything,” says UNC Health infectious diseases specialist Nikolaos Mavrogiorgos, MD.

Still, some people may push for a prescription, thinking they might get some benefit or at least it couldn’t hurt to try. Not only will antibiotics do nothing for a virus, but taking them unnecessarily could cause harm to you and your community. And it’s happening a lot—at least 28 percent of prescribed antibiotics are unnecessary, according to the Centers for Disease Control and Prevention (CDC).

We spoke to Dr. Mavrogiorgos about how antibiotics work and what people should know before taking them.

How Antibiotics Work

Antibiotics are prescribed for bacterial infections, including strep throat, ear infections, skin infections, abscesses, bladder infections and kidney infections. They work by killing the bacteria that cause these infections, going after the cell wall or membranes of bacteria or interfering with proteins in the bacteria and blocking bacteria reproduction.

“Some antibiotics target many different types of bacteria, while others target a more narrow group of bacteria,” Dr. Mavrogiorgos says. “We decide which is the most appropriate antibiotic based on a number of factors, such as the type of infection, risk factors for resistant bacteria, culture data and risk for side effects.”

Dr. Mavrogiorgos says antibiotics are essential in particular for serious bacterial infections that affect the function of vital organs and cause sepsis.

Although many common infections are caused by viruses, including the cold, flu and COVID-19, they won’t respond to antibiotics. Some symptoms of viral infections do overlap with bacterial infections. Strep throat, for example, is caused by bacteria, but most sore throats are caused by a virus, which is why your doctor will test you for strep. Sinus infections are typically viral but can be caused by bacteria. Sometimes, viral infections are immediately followed by bacterial infections. This confusion may be part of the reason people seek antibiotics when they aren’t necessary.

Antibiotics also don’t work on infections caused by fungi, including athlete’s foot, yeast infections and fungal nail infections.

Unnecessary Antibiotic Use Disrupts the Body’s Balance

If you take antibiotics when you don’t need them, they will not help you get better. What’s more, you put your health at unnecessary risk.

“Antibiotics are very safe, but they do have side effects, including sometimes serious ones,” Dr. Mavrogiorgos says. “They can cause rashes, diarrhea, nausea and vomiting. They can also affect kidney and liver function or cause an allergic reaction.”

If you need antibiotics, a doctor can help you consider the side effects and determine whether the benefits of the antibiotics outweigh the risks.

Also, because antibiotics kill bacteria, they upset the balance of “good” and “bad” bacteria in our bodies. Bacteria in our gut, for example, aid in digestion and keep harmful bacteria in check. “Antibiotics don’t discriminate between good and bad bacteria, so eliminating the good bacteria puts you at risk for certain conditions,” Dr. Mavrogiorgos says.

Most notably, taking a course of antibiotics can give Clostridioides difficile, or C. diff, a foothold, particularly if you are older than 65. The bacteria C. diff can be naturally present in the gut and cause fever, severe diarrhea, stomach pain and nausea. When beneficial bacteria are wiped out by antibiotics, C. diff can multiply. The condition can become life-threatening in more severe cases, and it’s also common to recur once you’ve had it.

Dr. Mavrogiorgos says it’s unlikely that you’ll be able to replenish those good bacteria by consuming probiotics, which are bacteria found in certain foods and supplements.

“It’s not clear whether probiotics will help very much, at least for prevention of C. diff,” he says. “There’s conflicting data, so while those foods and supplements won’t hurt, they probably won’t make much of a difference. You should discuss consuming probiotics with your doctor. In certain cases, such as significant immunosuppression, they can even cause harm.”

Unnecessary Antibiotic Use Builds Resistance to Treatment

Taking antibiotics unnecessarily can cause you to build a resistance to antibiotics, so they won’t work as well when you really need them.

Exposure to unnecessary antibiotics gives your body’s bacteria more chances to learn how to outsmart the medication. The bacteria can develop methods of destroying the antibiotic, or they can change so that the antibiotic is no longer functional in the body.

“As a result of exposure, the next time you have an infection that needs antibiotics, the bacteria may be more resistant to its effects,” Dr. Mavrogiorgos says. “You might have to use a stronger or broader antibiotic each time, but the problem is, the development of new antibiotics has slowed. It’s become critical to preserve the antibiotics we do have.”

If you become resistant to antibiotics, you may have to pursue more intensive treatments, such as receiving intravenous antibiotics or medications that come with more serious side effects.

The resistance also negatively affects other people. “When there are resistant bacteria in the community, they can spread to more people in different ways,” Dr. Mavrogiorgos says. “With more really resistant bacteria in the community, there will be more infections that will be very hard or sometimes impossible to treat. This is already a serious problem in other parts of the world.”

The CDC reports that more than 2.8 million resistant infections occur each year, with more than 35,000 people dying as a result.

Discuss Antibiotics with Your Doctor

Both providers and the people they treat can reduce the risk of antibiotic resistance by prescribing and taking antibiotics only when needed.

“It’s always good to have a discussion with your doctor when you’re prescribed an antibiotic,” Dr. Mavrogiorgos says. “You should understand why it’s needed. You can ask if for this particular infection it may be an option to use a narrow antibiotic, targeting specific bacteria, rather than a broad one that will affect a wide range of bacteria. You could also ask about whether it’s possible to use a shorter duration for your particular treatment. We have good data that a short duration of antibiotics is just as effective as a longer course for many common infections.”

Dr. Mavrogiorgos says your doctor may decide that one option is watchful waiting—not pursuing treatment but instead keeping a close eye on the infection—if you are stable and experiencing few symptoms and there is a chance the infection may resolve on its own. This can happen with some ear or sinus infections.

If your doctor prescribes an antibiotic, you should take it exactly as prescribed. Don’t share your antibiotics with others or save them for a future infection.

Feeling sick? Discuss your symptoms and possible treatments with your doctor. If you don’t have a doctor, find one near you.