Drug Interactions: What Foods, Drugs, Herbs Affect Medications?

Reviewed on 10/26/2021

Foods, Herbs, and Drugs Can Interact

Drug interactions can be dangerous for patients.

Medications can interact with other medications, both prescription and over-the-counter, but did you know that drugs can interact with foods, beverages, and herbs, too? A food, drink, drug, or herb may decrease or increase the effects of a medication, prevent it from working, or increase or decrease medication side effects. New side effects may emerge from an interaction. Make sure your doctor and pharmacist know all of the medications and herbs you are taking. If you are concerned that a food or beverage could affect a medicine you are taking, talk to your physician or pharmacist.

Grapefruit Dangers

Interactions between grapefruit and meds are possible.

Grapefruit is a common food that may affect more than 50 different medications by affecting their activity or metabolism. The nature of the interaction varies. The fruit may up blood levels of some medicines, like statins. In other cases, as with the antihistamine fexofenadine (Allegra), grapefruit and grapefruit juice decrease both the blood levels of the drug and its effectiveness. If you're unsure whether or not you can safely consume grapefruit and grapefruit juice with your prescription and over-the-counter medications, ask your doctor or pharmacist.

Dairy: Milk, Cheese, and Yogurt May Cause Problems

Dairy products can interfere with some meds.

Dairy products may interfere with the action of certain antibiotics. Calcium, magnesium, and casein (a protein in dairy products) may delay or prevent the absorption of certain types. If you are prescribed antibiotics, ask your physician or pharmacist whether or not you can safely consume dairy products while taking them. Remember to take the full course that was prescribed to get the maximum benefit. In other cases, a doctor or pharmacist may recommend the patient take some other drugs with milk or a bit of dairy to minimize the risk of upset stomach.

Think Twice About Licorice

Licorice has potentially dangerous interactions with some meds.

Licorice is flavoring that is found in gum, candy, and sweets. It is also an herbal remedy that soothes the stomach and aids digestion. Glycyrrhizin is a compound in licorice that may reduce the effectiveness of certain drugs, like the immunosuppressant cyclosporine. It is dangerous to take glycyrrhizin with digoxin, a medication used to treat heart conditions. The compound may provoke irregular heart beats or even a heart attack when taken with digoxin. Glycyrrhizin may also be dangerous if a patient has high blood pressure or other medical issues.

Chocolate Lovers: Think Twice

Chocolate has health benefits, but also potential interactions with drugs.

Chocolate is high in a compound called tyramine. Eating chocolate while taking an MAO inhibitor can lead to a dangerous rise in blood pressure (BP). Dark chocolate is high in caffeine which can interfere with the activity of medicines used to treat attention deficit hyperactivity disorder (ADHD) such as methylphenidate (Ritalin). Do not eat chocolate if you are taking sedatives or sleep aids, such as zolpidem tartrate (Ambien).

Use Care With Iron Supplements

Iron supplements interact with a long list of drugs used to treat a variety of conditions.

Iron supplements interact with a long list of drugs used to treat a variety of conditions. Cholesterol -lowering drugs including cholestyramine and colestipol interfere with the absorption of iron. So do acid blockers like ranitidine (Zantac), famotidine (Pepcid), and cimetidine (Tagamet). Conversely, iron decreases the absorption of some drugs including antibiotics like quinolones and tetracyclines and ACE inhibitors that treat high BP. Iron may reduce blood levels of thyroid replacement hormone (Levothyroxine) and Parkinson's treatments like carbidopa and levodopa (Sinemet). Birth control pills may increase blood levels of iron. Check your multivitamin. It may contain iron that can interfere with drugs you are taking. If you must take iron, ask your doctor or pharmacist how many hours before or after you should take it if you are on such medications.

Dangerous Interactions When Drinking Alcohol

Alcohol can be dangerous when you are on drugs for medical conditions.

Alcohol is a common substance that may interfere with a variety of drugs. Interactions with drugs may cause nausea, vomiting, fainting, headaches, dizziness, changes in behavior, and blood pressure changes. The effects of many other drugs are increased when consuming alcohol. Taking narcotics while drinking increases the risk of coma and death. Consuming it with nitrates may cause low blood pressure. The effects of sedatives, antidepressants, and antipsychotics are all increased with alcohol. It is dangerous to drink if a patient is taking acetaminophen or other pain relievers as it may cause liver damage. Patients who drink alcohol while taking nonsteroidal anti-inflammatory drugs (NSAIDs) increases the risk of stomach bleeding.

Is Coffee OK?

Interactions between coffee and meds are possible.

Caffeine in coffee is processed by the same liver enzymes as many drugs. These enzymes are known as the cytochrome P450 enzymes. Drinking coffee can interfere with the way active ingredients in certain meds are broken down. This may result in increased or even toxic levels of the meds. If you drink coffee, ask your doctor or pharmacist if it's safe for you to continue to do so if you are prescribed meds to treat asthma, depression, antibiotics, antiarrhythmics, antipsychotics, and agents for some skin disorders. Coffee can also interfere with the ability to absorb and utilize iron.

Allergy Meds

Drug interactions between antihistamines and other meds are possible.

Antihistamines prescribed for the treatment of allergies may interact with several meds. Antihistamines can make you tired, but if you take them with sedatives or tranquilizers, the combined effect can be even more exhausting. Allergy meds may interact with sedating antidepressants. The combined effect may impair your ability to drive and concentrate. Certain BP meds mixed with some antihistamines may cause a dangerous increase in blood pressure and heart rate. If you need to take a prescription or over-the-counter drug containing an antihistamine, speak to your doctor or pharmacist to make sure it doesn't interact with anything else that you're taking.

Antiseizure Meds

Interactions between seizure meds and other meds range from mild to severe.

Antiseizure meds have the potential to increase or decrease the blood levels of other meds. Antidepressants, antipsychotics, antibiotics, antivirals, antifungals, antiparasitics, birth control pills, blood thinners, antineoplastic drugs, and immunosuppressants are some of the meds whose blood levels may be affected if you take antiseizure meds. Potential drug interactions between antiseizure meds range from relatively mild to severe (for example, impaired thinking to increased number of seizures). Make sure your doctor and pharmacist have a complete list of the prescription drugs and over-the-counter meds you are taking and can check for potential drug interactions. Epilepsy is a serious medical condition. Take drug therapy as directed to minimize the risk of side effects and drug interactions.

Vitamin K and Blood Clots

High doses of vitamin K affect warfarin.

Warfarin is a blood-thinning medication used to help prevent blood clots. It is dangerous to consume too many foods high in vitamin K while you are taking warfarin. Excess levels of the vitamin will make warfarin and other blood thinners less effective and increase the risk of blood clots. Foods high in vitamin K include Brussels sprouts, parsley, kale, broccoli, and spinach. Even if you are not taking a blood thinner, ask your doctor which of these are safe for you to consume and in what amounts. Eat the same amount of foods rich in the vitamin every day to help keep levels in your blood steady so blood clotting is unaffected.

Ginseng and Blood Clotting

Drug interactions between ginseng and meds are possible.

Ginseng is an herb and dietary supplement that may promote bleeding and increase the effects of warfarin, heparin, and nonsteroidal anti-inflammatory drugs (NSAIDs). It is dangerous to consume ginseng when taking an MAO inhibitor because it may cause difficulty sleeping, nervousness, headaches, anxiety, and hyperactivity. Ginseng lowers blood sugar. Taking it along with diabetes medications that lower blood sugar or insulin may result in blood sugar that is too low.

St. John's Wort (Hypericum Perforatum)

St. John's wort can reduce blood levels of other meds.

St. John's wort is an herb is used to treat depression. It ramps up liver enzymes, so it may increase the metabolism of certain meds and lower their concentration in your bloodstream. Cholesterol-lowering meds including lovastatin (Mevacor and Altocor), sildenafil (Viagra) for erectile dysfunction, and digoxin (Lanoxin) prescribed for heart conditions are some of the meds whose concentrations may be lowered if a patient takes St. John's Wort at the same time. Depression is a serious medical condition. Seek professional help if you are depressed.

Gingko Biloba Drug Interactions

Patients who take gingko biloba may suffer from drug interactions.

Gingko biloba is an herb that promotes blood circulation and may help improve memory. Gingko may interfere with drugs prescribed to treat a variety of health conditions. High doses of the herb may make antiseizure medications like carbamazepine (Carbatrol, Equetro, Tegretol) and valproic acid (Depakote) less effective. Gingko may increase side effects of antidepressants, blood thinners, nonsteroidal anti-inflammatory drugs (NSAIDs). It may enhance BP medication, making blood pressure too low. It may make anti-anxiety medications less effective. Gingko may affect blood sugar, so take care and ask a health care professional before using it if you take diabetes drugs.

Read the Labels

Take meds as directed to protect your health and avoid drug interactions.

It is very common for patients to not take medications as directed. They may either take less than they need, skip doses, or take doses at random times. All of this is dangerous and makes it much more likely that medical conditions are not properly treated. Follow your health care professional's orders for taking prescription medications. Ask about potential interactions with other drugs and possible interactions with foods, herbs, and supplements. Meds need to be taken as directed to achieve the desired therapeutic effect.

Drug Interactions: What Foods, Drugs, Herbs Affect Medications?

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