Understanding drug interactions: How to keep your medications safe

Drug-drug interactions

Drug-drug interactions occur when one drug interacts with another.

Certain drugs are more prone to interactions than others. Drug interactions can occur because of how a drug is broken down in the body. They can lead to more or less of a drug being in the body, which can cause harmful effects.

In some cases, it may not be safe to take certain medications together. In other cases, you may still be able to take both medications, but the doses must be separated.

Quick tip: Before starting any new medication, including over-the-counter medications, talk with your doctor or pharmacist to make sure it is safe for you.

Example

Warfarin is an anticoagulant used to help prevent blood clots. It interacts with many other medications.

This is because a group of enzymes (called CYP450 enzymes) change the way the body metabolizes warfarin. Drugs that inhibit these enzymes can increase the effects of warfarin, increasing the risk of dangerous bleeding. Drugs that induce the enzymes reduce warfarin’s effectiveness, raising the risk of blood clots.

Supplement interactions

A 2019 poll from the American Osteopathic Association found that 86% of Americans take vitamins or supplements.

While supplements are beneficial for people with a deficiency, they still have potential side effects and interactions, just like any other medication. The supplements a person takes can interact with prescription drugs or other supplements.

For example, calcium can affect the absorption of certain drugs. This includes both calcium supplements and calcium-containing drugs, such as certain antacids. Calcium can affect the body’s ability to absorb the thyroid drug levothyroxine, which treats hypothyroidism.

Alcohol interactions

Alcohol can interact with many different drugs. It has the potential to interact with prescription drugs, supplements, and other recreational drugs.

Alcohol can interact with alcohol-containing drugs, such as cough syrup and laxatives. Consuming alcohol while taking these medications can intensify the effects of alcohol, which can be harmful.

It may also interact with other drugs that slow activity in the central nervous system, making a person sleepy. Some of these drugs include:

• antihistamines, such as diphenhydramine (Benadryl)
• benzodiazepines, such as alprazolam (Xanax) and lorazepam (Ativan)
• sleeping pills, such as zolpidem (Ambien)

Recreational drug interactions

Recreational drugs can cause drug interactions.

When a person takes cannabis with certain antipsychotic drugs, such as clozapine, it reduces the amount of the antipsychotic in their bloodstream. This makes the drug less effective, which can be dangerous.

Another example is that the commonly prescribed antidepressant citalopram (Celexa) can cause brain bleeding when taken with cocaine.

Food interactions

Certain foods affect how the body breaks down certain drugs. One common culprit is grapefruit.

An enzyme called CYP3A4 helps metabolize many drugs in the small intestine, but grapefruit blocks this enzyme. This makes more of the drug enter the bloodstream, resulting in a higher dose that stays in the body longer.

CYP3A4 levels vary from person to person, so it is difficult to predict how grapefruit might affect an individual. Some people might have no side effects at all, while others may experience life-threatening side effects.

Some medications that interact with grapefruit include:

• antihistamines, such as fexofenadine (Allegra)
• drugs used to lower cholesterol, such as simvastatin (Zocor) and atorvastatin (Lipitor)
• blood pressure drugs, such as nifedipine (Adalat and Procardia)
• anti-anxiety drugs, such as buspirone
• corticosteroids, such as budesonide (Uceris and Entocort EC)

Medical conditions and other factors

Certain medical conditions or other factors can make a person more likely to experience a drug interaction. A few examples include:

• High blood pressure: People with high blood pressure may want to avoid certain decongestants. Some of these, such as pseudoephedrine (found in many cold remedies), may increase blood pressure, making them an unsafe choice.
• Dementia: People with dementia are highly vulnerable to a number of drug interactions. One 2016 cross-sectional study found that antidepressants, antipsychotics, antiplatelets, and omeprazole were all more likely to cause interactions in older people with dementia. Frequently prescribed dementia medication was not a contributor to severe drug interactions.
• Genetics: People with certain genetic factors may be more prone to drug interactions. For example, some people may be poor metabolizers of certain enzymes (CYP) that help break down drugs in the body. This can put them at increased risk of side effects of the medication.
• Older adults: Aging impacts how the body processes drugs, which can cause medications to stay in your system longer or interact in unexpected ways. Older adults may also be more likely to take multiple medications, which can increase their risk for potential interactions.
• Multiple doctors: Seeing multiple doctors can lead to duplicate medications and drug interactions. It can be helpful to have a medication list to share with every doctor you have and to use one pharmacy for all of your prescription medications.

Be sure to talk with your doctor about all of your health conditions before starting any new medications.

Summary and next steps

Any food or substance can interact with any other substance, including medications you take every day. In some cases, these reactions can be very dangerous.

Ways to help prevent drug interactions include:

• Take only the drugs that are needed.
• Read all new drug labels thoroughly.
• Tell your doctor about all the medications, supplements, or substances you take.
• Talk with your doctor or pharmacist before starting any new medications.