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What happens if you don’t finish antibiotics?

Your doctor prescribed you a 10-day course of antibiotics for that nasty case of bronchitis, but you’re feeling better after five days. Do you still have to keep taking your prescription? Isn’t it better to not take medication you don’t really need?

Well, yes…and no! Antibiotics are powerful drugs designed to kill bacteria—think strep throat, ear infections, and urinary tract infections, among others—but they’re no good in the fight against viral illnesses. Taking an antibiotic when you have a virus like the common cold or flu won’t help you and, worse, it can actually do some harm.

“Taking antibiotics for a cold [is one of the things] that causes antibiotic resistance,” says Natalie Long, MD, a University of Missouri Health Care family practitioner. “When you do that, all the non-harmful bacteria in your body are exposed to the antibiotic and can adapt or evolve, making it harder for them to be killed by that antibiotic in the future.”

That said, if you’ve got a bacterial infection, you probably need an antibiotic to get rid of it—and yes, you need to take every single pill, regardless of how quickly you start feeling better. Here’s why.

How do antibiotics work?

According to Gwen Egloff-Du, Pharm.D., at Summit Medical Group in New Jersey, there are two types of antibiotics: bacteriostatic and bactericidal. Bacteriostatic antibiotics, like azithromycin and doxycycline, stop bacterial growth. Bactericidal antibiotics, like amoxicillin and cephalexin, kill the bacteria itself. 

When you show up sick at your healthcare provider’s office, your healthcare provider assesses your symptom history to determine if your illness is viral or bacterial. If you have a bacterial infection requiring antibiotic therapy, says Long, he or she will consider the organ system affected. Different parts of the body harbor different types of bacteria common to that location, so healthcare providers prescribe antibiotics that have a good chance of being effective there (i.e., ear infections are caused by different bacteria than UTIs, and will likely require a different kind of antibiotic). 

How does your healthcare provider determine duration of antibiotics?

Sometimes you take an antibiotic for five days, but sometimes it’s 14. What gives? 

Long says that treatments vary based on a number of factors, and the duration of antibiotic treatment is something that’s continually revisited by physicians and researchers

“Some infections are clear cut, like ear infections, and the duration is pretty standardized,” she explains. “Others, like UTIs, have a range of anywhere from three to 14 days based on how sick you are, whether you need to be admitted to the hospital, and how quickly you respond to the drug.” Another important determining factor is what other chronic conditions you may have chronically, such as asthma, diabetes, or heart disease.

But I’m feeling better…what happens if you don’t finish antibiotics?

Dr. Egloff-Du says there are two reasons why you need to take the full prescribed treatment of antibiotics. The first is obvious: Your healthcare provider selected the therapy for a reason, and that’s to get you healthy again. The second reason? The dreaded antibiotic resistance we mentioned earlier.

“By completing your course of treatment, you increase the odds of killing all the bacteria responsible for causing your current illness,” she says. “When you halt treatment early, you allow a small portion of bacteria to remain in your body and that bacteria has the potential to strengthen, change, and develop resistance.” 

So even if you’re feeling better after a few days, that doesn’t mean all of the bacteria which made you sick is actually gone yet. Per the Centers for Disease Control (CDC), antibiotic resistance is a major public health threat that affects upward of 2 million people every year. 

14 days is a long time! What happens if you miss a day of antibiotics?

Look, we’ve all been there—when you’re supposed to do something twice a day for two weeks, it’s not hard to forget about it at least once. In fact, it’s so common that Dr. Long says she actually considers this when she prescribes common antibiotics to patients (because it’s easier to remember one pill a day versus four!). 

So what should you do if you miss a dose of antibiotics? That depends on how long it takes you to realize your mistake.

“If you are a few hours late in taking your antibiotic, take it as soon as you remember,” advises Dr. Egloff-Du. “But if your next dose is due soon, do not double up.”

The general rule is if you are more than 50% of the way toward your next dose, you should skip. So for example, if you are supposed to take your antibiotic every 12 hours, you could take it if it’s less than six hours away from your next scheduled dose. If it’s beyond six hours, simply take the next dose when it’s due, understanding that your therapy will need to be extended to incorporate the dose you missed. (If you’re not sure what to do, remember that you can always ask your healthcare provider or pharmacist for assistance.) For people who struggle to remember their medication, Dr. Egloff-Du offers a few helpful tips. 

“Many patients find pill boxes helpful and others set alarms on their cell phone,” she says. “Combining [your dose] with one of your daily routines, like taking it when you eat breakfast at 8 a.m. every morning, can also be helpful.”

RELATED: The best pill reminder smartphone apps

If you miss several doses or days of therapy for any reason, Dr. Egloff-Du adds, it’s important to talk to your healthcare provider; likewise, if unpleasant side effects of antibiotics are deterring you from taking your prescription, you should also pick up the phone—your healthcare provider  may be able to suggest an alternative therapy.