Dietary considerations: how food and supplements affect your meds

Food, drinks, and over-the-counter supplements can change how a medicine works — sometimes making it weaker, stronger, or causing side effects. A few small habits keep you safe: tell your pharmacist about every pill and herbal product you take, follow directions about taking meds with or without food, and keep a consistent diet when on drugs that need steady nutrients.

Common food–drug pairs to watch

Grapefruit juice: don’t assume it’s just a snack. Grapefruit can raise blood levels of many drugs, which may increase side effects for some cholesterol and blood-pressure medicines. If a label warns against grapefruit, avoid it and grapefruit juice entirely.

Dairy, calcium, and iron: antibiotics like tetracyclines or fluoroquinolones bind to calcium and iron in milk or supplements and won’t absorb well. Take these antibiotics 2–4 hours apart from dairy, calcium, or iron supplements.

Herbal supplements: St. John’s wort, valerian, and kava can change antidepressants and other brain-active drugs. St. John’s wort speeds up liver enzymes and can make meds like citalopram (Celexa) or certain birth controls less effective. Valerian or kava can add drowsiness if you’re already on sedating meds.

Alcohol and certain meds: alcohol plus metronidazole or some painkillers can cause nausea, flushing, or worse. If you’re prescribed metronidazole, skip alcohol during treatment and for at least 48 hours after.

Potassium and blood pressure meds: drugs like losartan can raise potassium. Using potassium supplements or salt substitutes high in potassium can cause dangerous levels. If your doctor prescribes an ARB or ACE inhibitor, check your potassium intake.

Simple habits to stay safe

Keep one up-to-date list of everything you take — prescriptions, vitamins, herbs, and even protein powders. Share that list with every provider and your pharmacist.

Read the label: if a medicine says “take on an empty stomach,” it usually means one hour before or two hours after food. If it says “take with food,” do so to cut stomach upset and improve absorption.

Ask targeted questions: "Can I drink grapefruit or alcohol with this?" "Do I need to separate this from my calcium or iron?" Pharmacists are great at answering those fast.

If you change your diet — start a high-protein plan, add a lot of leafy greens, or take new supplements — check how that might affect medicines like blood thinners, heart drugs, or antidepressants. Small changes can matter.

When in doubt, pause the supplement and ask. Many natural products are useful, but they’re not always safe with prescription drugs. A quick call to your healthcare team can prevent a bad interaction and keep your treatment working as intended.