Our medications are meant to keep us healthier. But chances are good that at some point or another, you’ve made a seemingly innocent medication mistake that put your health at risk.

“It’s not hard to make a variety of mistakes with your prescription, including not taking it at the right time [or] taking too little or too much,” says Sarah, MD, president of the American Academy of Family Physicians. Here’s a handy guide to help you avoid six top medication mistakes.

Cutting or crushing the wrong pill or capsule

Have you ever noticed some drugs cost the same or almost the same no matter the dosage? That means your doctor could prescribe a 40-milligram Cholesterol pill and have you cut it in half if you only need 20 milligrams, saving you a ton of money.

But not all pills are safe to cut in half. If the Food and Drug Administration has approved a pill for splitting, it will say so on the package insert. Pills that are scored down the middle are easier to split in two, but your doctor or pharmacist should still give the green light before you do so. Avoid splitting capsules, pills with a hard outer coating, extended release formulas or pills that are small and uneven. Your body may not absorb the medicine properly if you split pills with a hard outer coating or an extended release formula. Small, uneven pills are difficult to split, so you might get too much or too little in one dose.

Most pills are not meant to be crushed before being swallowed. (Some people do this to long-acting painkillers to get high.) “Long-acting medications usually have a special coating which serves to release the drug gradually. But when people crush pills, they end up ingesting a large dose all at once, which can be potentially fatal,” says Sarah. Also, if the capsule has a coating that’s designed to protect your stomach, you risk stomach irritation if the outer layer is damaged.

Tempted to crush a capsule because it’s too big for you to comfortably swallow? Don’t. Try this trick instead, inspired by a new German study that looked at the best techniques for swallowing pills: Fill a regular-size soda bottle with water. Put the capsule on your tongue, then close your lips tightly around the bottle’s opening. Tilt your head back, suck the water and pill into the back of your throat and swallow.

Not taking the medication as directed

Have you ever stopped taking your antibiotics halfway through your prescription because you felt better? That’s a major no-no. While the first few days of the drug might have wiped out some of the bacteria, it’s not all gone, and the infection could come back if you stop.

There’s another problem with stopping too soon. “If you’re given a 10-day course [of antibiotics] to take, but you feel better after 7 and then stop taking it, you may increase the risk of drug resistance,” Sarah says. This means the germs that weren’t wiped out by day 7 have developed some resistance to the drug. This is, in essence, is how super-bugs develop.

If you think you don’t need a medication anymore, always check with your doctor before stopping it. Some drugs, like certain antidepressants, need to be tapered off gradually.

Some people skip doses because they can’t afford their medications. If that’s you, ask your doctor for advice on how to get free or low-cost medication.

Forgetting doses

For some medications, missing a single pill or spoonful won’t create major problems. “But for certain drugs, such as those that control seizures or help to prevent blood clots, a skipped dose can actually make the drug ineffective,” says Sarah.

Check the drug information that came with your prescription for what to do if you miss a dose. (Don’t just take a double dose the next time.) If you’re not sure what to do, call your doctor or pharmacist.

A woman who misses a dose of her oral contraceptive should take it as soon as she remembers. More than one missed pill ups the risk of pregnancy, so be sure your partner wears a condom.

Doubling up on active ingredients

You’re taking a painkiller that contains acetaminophen (the active ingredient in Tylenol). But you don’t realize that your cold medicine contains it, too — and your liver may pay the price.

“Acetaminophen, which is found in pain relievers, cold medicines and sleep aids, is a classic example of a doubled-up ingredient, which in this case may cause liver damage if the dose is too high,” says Sarah.

Check medicine labels to make sure you’re not taking two different drugs with the same active ingredient, unless your doctor told you to. And always get in touch with your doctor right away if you notice any unusual side effects.

Combining the wrong drugs

Some medications don’t play well with others. If you buy all your prescription medicines from the same pharmacy — a good idea — the pharmacist should know and alert you if two of your prescriptions may interact badly.

But over-the-counter medicines and even vitamins and other can also change the way a prescription drug behaves. Antihistamines for a runny nose or allergies, for example, often react badly with sedatives or tranquilizers, or with a prescription drug for high blood pressure or depression. Acid reducers for heartburn can cause problems when taken with medicines containing cimetidine, used in asthma pills, the blood-thinning drug warfarin or phenytoin, a drug used for seizures. So don’t use those meds in combination unless your doctor tells you to, and always tell your doctor (and your pharmacist to be safe) about everything you take.

“Make sure your doctor knows about every single medication you’re on, such as OTCs, vitamins, supplements, and herbs,” says Sarah. An easy way to do this: Throw all your prescription meds and OTCs into a bag and bring it with you to your next appointment.

Sharing medications with friends and family

Some well-meaning people may give their friends, say, a prescription pain drug if they’re aching all over, but it’s a colossally bad idea (not to mention illegal). Not only could the drug harm them or interact with something else they’re taking, but you would be partly responsible if something went wrong.