At one point or another, most of us have been prescribed antibiotics to help treat a bacterial infection. Maybe you had a sinus, skin or ear infection or a chest cold that just wouldn’t let up. But if you didn’t follow the pharmacist’s recommendation on how to take antibiotics, without realizing it, you were asking for trouble.

Here are five common and potentially serious mistakes people make when taking antibiotics.

1. You stop taking antibiotics as soon as you feel better. Your doctor gives you seven to 10 days worth of pills. But you feel better within the first few days of taking the medication, so you stop the antibiotics. This is one of the worst things you can do when you’re trying to fight off a bacterial infection. You might be feeling good, but your body is still under bacterial attack. The first few days of antibiotics might have slowed or lowered your infectious bacteria load. But to effectively wipe out infection-causing bacteria you need to finish the prescription. Even more reasons to stay the course: When you stop taking an antibiotic before all of the bacteria are gone, bacteria can come back in higher numbers and also become much stronger. As a result, you might need to repeat the entire course of the medicine, or take a stronger antibiotic to get the infection under control. This pattern of misuse is also one of the key contributors to antibiotic-resistant bacteria. Essentially, bacteria are learning how to outsmart antibiotics, which creates stronger harder to treat bacteria and medicines that are much less effective.

2. You stop taking antibiotics because they make you nauseous. Unfortunately nausea is a common side effect when taking antibiotics. But there are lots of things you can do to lessen nausea. First, check with your pharmacist or doctor to make sure you’re taking the medication properly. Let her know that your stomach is bothering you since starting the antibiotic. She may recommend taking the medicine with or without food, avoiding dairy or adding a probiotic to help ease some of the stomach queasiness.

3. You hoard the pills you didn’t take, thinking you’ll save them for next time. This is a bad idea for a lot of reasons. First, it means you’ve stopped taking your antibiotics before they are gone. (See mistake #1, above.) And now you’re acting as your own doctor. Deciding if you need an antibiotic, and if so which one, should be left to the professionals. Taking an antibiotic when you don’t need one, or taking the wrong one for your illness, helps create more antibiotic-resistant bacteria. 

4. You share with a friend. Giving your friend some of your antibiotics hoping it’ll help with her sinus infection, too, means you miss out on the full course of medication. And because antibiotics cause different reactions in different people, it’s never smart to share. Allergic reactions to antibiotics can be really serious or deadly. 

5. You give the wrong info about antibiotic allergies. When choosing the right antibiotic your doctor will ask if you have any drug allergies. Sounds like an easy enough question — but you’d be amazed how many people get it wrong. Not on purpose, of course; some of us have just taken our parents’ word for it all these years that we are or aren’t allergic. Others think side effects, such as nausea or vomiting, are an allergy. In fact, one study presented to the American College of Allergy, Asthma, and Immunology found that 94 percent of those who thought they were allergic to penicillin were not. Knowing your allergy history allows your doctor to prescribe you the best, safest treatment. For a lot of simple bacterial infections, penicillin is considered the best and cheapest treatment. People who mistakenly think they are allergic to penicillin may be limit themselves to a less effective, more expensive antibiotic option. If you think you’re allergic to an antibiotic, see an allergist to have it confirmed before it goes on your medical chart.