OTC Medicines: Know Your Risks and Reduce Them

Last Updated August 2022 | This article was created by editorial staff and reviewed by Robert "Chuck" Rich, Jr., MD, FAAFP

Over-the-counter (OTC) medicines are those you can buy at the store. You don’t need a prescription from your doctor. They help you feel better by treating or preventing common health problems. These could include pain, allergies, constipation, cold and flu, or nausea. But sometimes OTC medicines can cause unpleasant effects. These are called adverse effects. They include:

  • Side effects
  • Drug-drug interactions
  • Food-drug interactions
  • Allergic reactions

It is best to be aware of the risks of OTC medicines so that you know how to avoid them.

Side effects

Side effects are effects that medicines have on your body that don’t help your symptoms. Most side effects are unpleasant. A few examples are nausea, dizziness, or bleeding in your digestive tract. Sometimes, side effects can be useful. For example, certain antihistamines can cause sleepiness. This might be bad for people who take antihistamines during the day. But if you’re taking an antihistamine at nighttime, this side effect might help you get the sleep you need. Side effects are not the same thing as true drug allergies. Those are much less common.

Drug-drug interactions

The body processes every medicine differently. When medicines are used together, the ways they affect the body can change. This is called a drug-drug interaction. It happens whether they are prescription or OTC medicines. It can increase the chance that you will have side effects from medicines you are taking. The main interaction types are:

  • Duplication: This is when you take 2 medicines that have similar active ingredients. It can give you more medicine than you need. An example is when you take OTC ibuprofen (Advil, Motrin) plus a prescription anti-inflammatory medicine. Too much of either an anti-inflammatory or pain reliever can hurt your kidneys or liver.
  • Opposition: Medicines with active ingredients that have opposite effects on your body can interact. This may reduce the effectiveness of 1 or both medicines. For example, OTC decongestants may raise your blood pressure. This can work against (cause opposition to) medicines that lower your blood pressure.
  • Alteration: One medicine may change the way your body absorbs, spreads, or processes another medicine. For example, aspirin can change the way some prescription blood-thinning medicines work.

If you see more than 1 doctor, tell each of them about the medicines you take. Do this even if you take something for just a short time. Include any herbal supplements, vitamins, and minerals you take. Once a year, take all of your medicines and supplements with you when you see your doctor. You should also do this if your medications change at any time.

Drug-food interactions

Food may change how your body processes some OTC or prescription medicines. This is called a drug-food (or drug-nutrient) interaction. Sometimes the things you eat and drink can affect the ingredients in a medicine you’re taking. This can prevent the medicine from working the way it should. For example, medicines taken by mouth are usually absorbed through the lining of the stomach. The nutrients from the food you eat are also absorbed this way. If you take a medicine with food but the directions say not to, your body might not be able to absorb the medicine the right way.

Food does not affect all OTC medicines. But what you eat and when you eat it does matter with some medicines. This is why some medicines should be taken on an empty stomach. That means 1 hour before or 2 hours after eating. At the same time, some medicines are absorbed or processed better when you take them with food.

Read the drug facts label carefully. See if you should take your medicine with food or on an empty stomach. If the label doesn’t give specific instructions, it probably doesn’t matter when you take it. If you have any questions, ask your family doctor or pharmacist. They can also warn you about possible interactions with your prescription medicines.

Allergic reactions

It’s not common, but some people are allergic to certain medicines. Signs of an allergic reaction include itching, rash, hives, and breathing problems. If you’ve ever had an allergic reaction to a medicine, avoid medicines that contain the same ingredients. Call your doctor or seek immediate medical help if you think you’re having an allergic reaction. Keep in mind that side effects are not true allergic reactions.

Path to Improved Health

Certain situations put you at higher risk for adverse effects. The possible adverse effects differ from 1 OTC medicine to another, so it’s best to carefully read the drug facts label of any OTC medicine. Then you will know what to expect.

Here are some more tips to help you avoid adverse effects.

  • Try to limit how often you use OTC medicines. Don’t use them unless you really need them.
  • If you take any prescription medicines, ask your doctor before taking an OTC medicine.
  • Read the drug facts label on the medicine carefully. Make sure you know what ingredients the medicine contains. Also make sure you understand any warnings or possible adverse effects.
  • If you don’t understand something about the medicine, ask your doctor or pharmacist.
  • Take the medicine just as your doctor or the drug facts label instructs. Don’t take a higher dose of the medicine than recommended. Don’t take the medicine more frequently than the label says. Don’t take it for a longer period of time than recommended.
  • When giving medicine to children, use the correct measuring device to make sure they get the right amount. This could be a spoon made for measuring medicine, or a syringe or cup.
  • Don’t take capsules apart or stir medicine into your food unless your doctor says it’s okay. This may change the way the medicine works.
  • Don’t take medicine with alcoholic drinks.
  • Don’t mix medicine into hot drinks unless the label tells you to. The heat may keep the medicine from working as it should.
  • Don’t take vitamin pills at the same time you take medicine. Vitamins and minerals can cause problems if taken with some medicines.
  • Keep track of any allergies and adverse reactions you have had to OTC medicines in the past. Avoid medicines that contain the same ingredients.
  • Check drug facts labels and avoid taking medicines that contain the same active ingredients at the same time. This can help you avoid taking too much of a certain medicine.
  • Remember that even if you took a medicine in the past with no problems, you could still have a reaction when you take it now.

Things to Consider

Healthy adults who use OTC medicines occasionally and properly have a low risk of adverse effects. However, some people are at greater risk. These include very young children, older adults, and people taking more than 1 type of medicine. People who have the following conditions are also at a higher risk:

  • Asthma
  • Bleeding disorders
  • Blood clotting disorders
  • Breathing problems
  • Diabetes
  • Enlarged prostate glands
  • Epilepsy
  • Glaucoma
  • Gout
  • Heart disease
  • High blood pressure
  • Immune system problems
  • Kidney problems
  • Liver problems
  • Parkinson’s disease
  • Psychiatric problems
  • Thyroid problems

These conditions put some people at greater risk. But anyone can experience an adverse effect from an OTC medicine.

How will I know if I’m experiencing an adverse effect?

Anytime you take medicine, be aware of changes in your body and how you feel. A certain symptom may be caused by your illness, or it may be an adverse effect from your medicine. It may be hard to know the difference. Tell your family doctor when the symptom started. Tell them if it is different from other symptoms you have had.

Are older adults at increased risk for adverse effects?

Older adults often use many medicines at the same time. This often includes both prescription and OTC medicines. Their bodies process medicines differently than younger adults. This is why they need to pay careful attention to drug-drug interactions. If you are an older adult, talk with your doctor about all of the medicines you take. This includes OTC medicines, vitamins, and herbal supplements. Your doctor can tell you whether you are at risk of having an adverse effect from taking an OTC medicine.

Questions to Ask Your Doctor

  • What are the interactions between the medicines I take?
  • Should I take any of my medicines with food or on an empty stomach?
  • Do I need to tell my doctor about the vitamins I take regularly?
  • Should I tell my doctor every time I take a new OTC medicine?
  • What kinds of symptoms should I look out for that could mean I’m having an adverse reaction to my OTC medicine?
  • Is my symptom a side effect or a true allergic reaction to a medicine?


U.S. Food and Drug Administration: Finding and Learning about Side Effects (adverse reactions)


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