If you take cholesterol medication, you probably know to avoid grapefruit juice. That's just one example of a potentially dangerous food and drug combination.

If you take cholesterol medication, you probably know to avoid grapefruit juice. That’s just one example of a potentially dangerous food and drug combination.

Food can interfere with drugs in different ways. Sometimes the way the body handles the food and the drug is too similar. Other times there’s a chemical reaction that can increase or decrease the absorption of the drug. In any case, the drug does not work as intended. The body tends to react to drugs as a foreign or toxic compound, so it tries to get rid of them. For some drugs, enzymes from foods change the structure to make the drug dissolve in water, making it possible to excrete it through bile or urine. Interactions also can occur between over-the-counter drugs and prescription drugs. The prescription label or information sheet might note these interactions, and the pharmacist might also inform you.

Following are five of the most common dangerous food-drug interactions.

1. Calcium-rich foods and antibiotics. Some antibiotics, such as doxycycline and ciprofloxacin, can bind with calcium, forming an insoluble substance that the body is unable to absorb. This makes the antibiotic ineffective and can contribute to antibiotic resistance. Calcium in dairy foods, as well as in multivitamins or other supplements, should not be consumed near the same time as the antibiotic.

2. Pickled, cured or fermented foods, and MAO inhibitors. These foods contain tyramine, which has been associated with a dangerous increase in blood pressure among patients taking monoamine oxidase inhibitors (MAOIs) and certain medicines for Parkinson’s disease. MAOIs are used to treat depression, although they have fallen out of favor because of this potential interaction. Tyramine-containing foods include soy sauce; sauerkraut; chocolate; salami and other aged cured meats; aged cheese; dried fruits; and alcohol.

3. Vitamin K-rich foods and warfarin. Warfarin, commonly known as Coumadin, thins the blood, in part by blocking the absorption of vitamin K, which the body needs to make a blood clot. If you consume a lot of vitamin K, it could overwhelm the drug. But it would take a lot of vitamin K foods to do that. Many people on Coumadin are told never to eat anything green, but this is not the current recommendation. Rather, you should maintain a consistent intake of vitamin K foods and just avoid introducing new sources of vitamin K into your diet. If you like to eat dark leafy greens, such as spinach or kale, on a regular basis, go ahead and do so. Just avoid a sudden and significant increase or decrease in your vitamin K intake, which could cause problems.

4. Alcohol and prescription stimulants. You should always be wary of mixing any medication with alcohol. Some interactions are more serious than others. Alcohol can affect the central nervous system, liver and kidneys. If you mix alcohol with a drug that also affects the central nervous system, either the drug’s effect or the alcohol’s effect might be amplified. If you have several drinks every day, you may have more enzymes than normal to metabolize alcohol. This might result in medications being broken down faster than they should be and not having time to work properly.

5. Grapefruit and several medications. Compounds in grapefruit can destroy one of the main enzymes that metabolize statins and other drugs. This means the drug won’t be fully metabolized, intensifying the strength of the drug in the body. This can cause side effects such as muscle pain. With some allergy medications, grapefruit and some other fruit juices can inhibit the transporters that the drugs use to get in and out of cells, resulting in less drug absorption. Other medications affected by grapefruit include antihistamines, blood pressure drugs, thyroid replacement drugs, birth control, stomach acid-blocking drugs and cough suppressants. Avoid grapefruit in any form when taking these medications. Follow these recommendations for all medications you take, including over-the-counter and prescription medications, as well as supplements:

Read the prescription label and all information sheets with your medication. Ask the pharmacist if you have a question. Take special note of all warnings and precautions, and carefully follow all directions for taking the medication.

Take all medications with a full glass of water, unless instructed otherwise.

Do not take capsules apart or stir the contents into food without a doctor’s or pharmacist’s approval.

Do not mix medications with hot drinks. Never take medications with alcohol. Notify your doctor and pharmacist of all over-the-counter and prescription medications you routinely take, as well as all vitamins, supplements and herbal remedies.