Food and Drink Interactions With Medicines: Grapefruit, Vitamin K, Tyramine, Alcohol

Grapefruit

FDA explains that grapefruit juice can block an intestinal enzyme called CYP3A4 that helps break down many medicines, so more of the medicine can enter the blood. [1] For certain cholesterol-lowering statins, FDA says too much medicine can stay in the body and raise the risk of liver and muscle damage that can lead to kidney failure. [1] The effect varies between people because the amount of this enzyme varies. [1] It does not affect every medicine in a class, and for fexofenadine the juice can lower absorption instead. [1]

FDA adds that pomelos and tangelos might have the same effect as grapefruit juice. [1] It points readers to the Drug Facts label and the pharmacist. [1] Other sources name specific medicines: MedlinePlus advises avoiding grapefruit with cyclosporine and the NHS says no grapefruit juice with diazepam or warfarin. [2] [3] [4] More on citrus fruits and the grapefruit page.

Vitamin K foods and warfarin

The NHS says foods high in vitamin K, such as broccoli, spinach and other green leafy vegetables, can affect how warfarin works. It adds that you can still eat them but should ask the warfarin clinic for advice. [4] MedlinePlus says to eat consistent amounts of vitamin K foods week to week and to talk to your doctor before changing the diet. [5] The NHS also names cranberry juice and cranberry products, and large amounts of alcohol, in its warfarin advice. [4] See leafy greens, natto and vitamin K.

Tyramine and MAOI antidepressants

MedlinePlus pages for the MAOI medicines phenelzine and tranylcypromine warn of a serious reaction with foods high in tyramine. They say tyramine is in many foods, including meat, poultry, fish or cheese that has been smoked, aged, improperly stored or spoiled. [6] [7] They say the doctor or dietitian will say which foods to avoid completely and which can be eaten in small amounts. [6] NIAAA notes that the risk of dangerously high blood pressure rises when MAOIs are mixed with tyramine, a byproduct found in beer and red wine. [8] MedlinePlus also says to avoid caffeine-containing foods and drinks with phenelzine. [6] Supplements can matter too: MedlinePlus lists tryptophan among products that may interact with phenelzine. [6]

Alcohol

Alcohol is a drink that interacts with many medicines. NIAAA says mixing it with certain medicines can cause drowsiness, fainting, loss of coordination and internal bleeding, and can make a medicine less effective or harmful. [8] It adds that some herbal remedies can have harmful effects with alcohol. [8] For warfarin, NIAAA says even occasional drinking may lead to internal bleeding. [8] The sleep-medicine and acetaminophen details are on the sedatives page and the pain medicines page.

Other examples named in sources

• Caffeine and diazepam. The NHS says caffeinated drinks can sometimes reduce the effects of diazepam. [3]
• Lithium, fluid and salt. MedlinePlus says to follow a proper diet with the right amounts of fluid and salt during lithium treatment. [9]
• Fruit juice and fexofenadine. FDA says orange or apple juice may also reduce how well fexofenadine works. [1]

What this page does not cover

Proper evidence not found in the pages we read for food interactions with most herbal supplements; the sources we read focus on medicines. That is a gap in what we read, not proof of safety. For foods and spices in their own right, see functional food safety.

Who should ask first

NIAAA says older people are at particularly high risk from alcohol-medicine interactions. [8] Anyone on warfarin, an MAOI, cyclosporine or lithium should check the leaflet and ask the pharmacist before diet changes. [4] [6] [2] [9]