Food, Supplements, Medication, and Conditions

A drug interaction occurs when a substance affects the behavior of a drug in the body. Some substances that can cause interactions include other drugs, supplements, foods, and alcohol.

Drug interactions can make a drug less effective. In some cases, they can make a medicine more potent, which can be dangerous.

The symptoms Drug interactions vary widely and range from mild to fatal. Some common warning signs include feeling sick after taking a medicine, not getting the usual results from a medicine, or feeling very tired or very energetic after taking a medicine.

Drug interactions don’t just happen between prescription drugs. Over-the-counter drugs, foods, supplements, and alcohol can all change the way the body metabolizes (breaks down) drugs.

Learn more to learn more about the different types of drug interactions, risk factors, and how to help prevent interactions by carefully reading drug labels.

There are several types of drug interactions.


Drug interactions occur when one drug interacts with another.

Some drugs are more prone to interactions than others. For example, warfarin is a blood thinner used to help prevent blood clots. It interacts with many other drugs.

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

These potentially harmful results show how important it is to discuss new drugs with a doctor or pharmacist.


A 2019 American Osteopathic Association survey 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 drug. The supplements that a person takes can interact with prescription drugs or other supplements.

For example, calcium can affect the absorption certain drugs.

This includes both calcium supplements and medications that contain calcium, such as some antacids. Calcium can also affect the body’s ability to absorb thyroid medication, levothyroxine, which treats hypothyroidism.

When discussing medications with a doctor, a person should be sure to write down the vitamins, supplements, and herbal remedies they are taking.

Alcohol and other recreational drugs

Alcohol and recreational drugs interact with many different drugs. They can interact with prescription drugs, supplements, and other recreational drugs.

Alcohol can interact with medicines that contain alcohol, such as cough syrup and laxatives. Drinking alcohol while taking these medicines can make the effects of alcohol more intense, which can be harmful. It can also interact with other drugs that slow down the activity of the central nervous system, making a person drowsy. Some of these drugs include:

Recreational drugs can also 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 medicine less effective, which can be dangerous. Citalopram (Celexa), a commonly prescribed antidepressant, can cause brain hemorrhage when taken with cocaine.

People with mental health problems are more likely have a substance abuse disorder. This means that the medication they are taking to treat their mental health problem may not be as effective if they also have an addiction disorder. If a person or loved one is concerned about mental illness and addiction, they should contact a doctor or one of the organizations below:


Certain foods affect the way the body metabolizes certain drugs.

A common culprit is grapefruit. a enzyme called CYP3A4 helps metabolize many drugs in the small intestine, but grapefruit blocks this enzyme. This causes more of the medicine to 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 may not have any side effects. Others may experience life-threatening drug toxicity.

Some drugs that interact with grapefruit include:

Find out more about the interactions between grapefruit and statins, which are used to lower cholesterol and treat heart disease.

Medical conditions

Certain medical conditions can make a person more likely to experience a drug interaction.

For example, people with high blood pressure may want to avoid certain decongestants. Some of these, like pseudoephedrine (found in many cold remedies), can raise blood pressure, making it a dangerous choice.

In addition, people with dementia are very vulnerable to a number of drug interactions. A 2016 transversal study found that antidepressants, antipsychotics, antiplatelet drugs, and omeprazole were all more likely to cause interactions in older people with dementia. Frequently prescribed dementia medications have not contributed to serious drug interactions.

People with certain medical conditions, especially those requiring regular medication, should contact a doctor before starting any new medication. This reduces the risk of potentially harmful drug interactions.

The more medications (including supplements) a person takes, the greater their risk of drug interactions.

People who take many different medications should read the label of each medication. They should also consult a doctor or pharmacist about any potential interactions.

Some people are more vulnerable to drug interactions than others, regardless of the number of medications they take. Factors that increase a person’s risk of drug interactions include:

Reading drug labels carefully can help prevent drug interactions. If a person is confused or concerned about a potential interaction, they should contact a doctor.

The labels of supplements and prescription drugs are different.

Prescription drugs should list known drug interactions. Drug labels usually list the most serious and common interactions. They may also have an insert with a title that says “Drug Interactions”. A person should read this section carefully.

Supplement drug labels must be precise and not misleading. But there is no obligation for them to list all drug interactions. People who take supplements should tell their providers about any supplements they take.

One of the best ways to reduce the risk of drug interactions is to consult a doctor before taking any new medication, including supplements.

Contact a doctor if:

  • a new medicine does not work or produces an unexpected result
  • a person becomes ill or develops unusual symptoms, such as drowsiness
  • a person wants to try a new supplement

Go to the emergency room if:

  • a person has signs of a serious reaction, such as a rash, difficulty breathing, or lethargy
  • a person takes a dangerously high dose of a medicine
  • a child uses supplements or prescription drugs

Any food or substance can interact with any other substance. In some cases, these reactions can be very dangerous.

The best way to avoid drug interactions is to take only the medications you need and to read all new drug labels carefully.

If a person is unsure or has concerns about a potential drug interaction, they should contact a doctor or pharmacist.

When a person takes a new prescription, they should ask questions about common drug interactions and let the pharmacist know about any other medications and supplements they are taking.

People who have negative reactions to medications should talk to a doctor right away.

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