Prednisone is one of the most prescribed medications in the US, with about 17.8 million prescriptions dispensed to roughly 10 million patients in 2024, according to ClinCalc DrugStats. Yet many patients fill that prescription without ever hearing that certain everyday foods can affect medications, amplifying side effects or altering how the drug works.
Clinical pharmacists point to a small set of dietary culprits. The Drugs.com food-interaction database and guidance from clinical pharmacists at University Hospitals flag licorice, grapefruit, high-sodium foods and sugary foods as the main concerns for anyone on prednisone or a related corticosteroid.
Licorice can dangerously lower potassium
Black licorice is not just a candy. Its active compound, glycyrrhizic acid, can slow the breakdown of prednisone and push potassium down at the same time. "Licorice can slow the breakdown of the medication, raising levels in the bloodstream while lowering potassium," Dr. Yongjin Chen told University Hospitals.
Chronic licorice intake can trigger pseudohyperaldosteronism, a condition marked by low potassium, high blood pressure and metabolic alkalosis. Since prednisone already depletes potassium and raises blood pressure, the two effects can stack.
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The warning covers black licorice candy, licorice extract in some herbal teas and diuretics, and any product that lists glycyrrhizin or glycyrrhizic acid on the label.
Grapefruit may raise drug levels in your blood
Grapefruit inhibits an enzyme in the gut wall called CYP3A4, which helps break down many oral medications, including corticosteroids. When that enzyme is blocked, more of the drug can reach the bloodstream, in effect raising the dose.
The strength of the interaction varies from person to person and between brands of juice, and the clinical evidence is stronger for methylprednisolone than for prednisone itself. Even so, standard prescribing guidance still advises limiting grapefruit and grapefruit juice during treatment and watching for side effects.
Salty foods worsen fluid retention
Prednisone acts on kidney receptors in a way that causes the body to hold on to sodium and water. That is why puffiness, weight gain and higher blood pressure are common on the drug.
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Piling salty food on top of that effect pushes blood pressure up further. Standard advice is to go easy on processed meats, canned soups, salty snacks and fast food, and to cook more meals from scratch where the salt is under your control.
Sugary foods pile on the blood-sugar spike
Prednisone raises blood sugar through several mechanisms, including impaired insulin secretion, increased insulin resistance and higher glucose output from the liver. Anyone on the drug can develop steroid-induced hyperglycemia, and people with diabetes often see their numbers climb.
Loading up on sugary drinks, desserts and refined carbohydrates on top of that effect makes control harder. Trading soda and sweets for whole fruits, vegetables and whole grains gives the same energy without the sharp spike.
What to eat instead
Corticosteroids also pull calcium from bones over time. The National Institute of Arthritis and Musculoskeletal and Skin Diseases lists glucocorticoids among medications that raise the risk of osteoporosis, and recommends a diet rich in calcium and vitamin D to help protect bone density.
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That points to a simple pattern for people on prednisone. Low-sodium meals, calcium-rich foods such as dairy, leafy greens and fortified plant milks, and complex carbohydrates instead of refined sugar.
Anyone unsure about how to adjust their diet, or concerned about side effects, should talk to their doctor or pharmacist before changing what they eat or how they take the drug.
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This article is made and published by Jesper Bengtson, who may have used AI in the preparation.