The Dangers of Food & Drug Interactions

By Dr Kamal ‘Akl,

Consultant Paediatrician & Paediatric Nephrologist

When I prescribe medicine for a child, few parents ask me questions concerning medicine and food interactions. It’s important to know that medicine may interact with other drugs, herbs, supplements and food.

Food may be functional and interact with medicines in different ways. It may decrease or increase the absorption of a specific drug from the intestine or interfere with the mode of action, leading to unwanted side effects.


High-fat food may increase the absorption of  certain antifungals

High-protein food may interfere with various medications

High-fibre food can reduce the effect of specific medicines, because these drugs can bind to the fibre in the food. This reduces drug absorption, thus decreasing the medicine’s effect

Any food can interfere with the absorption of osteoporosis drugs

Dairy products

Milk and yoghurt are rich in calcium which may bind to certain antibiotics producing an insoluble substance. Dairy products  decrease iron absorption. So one should wait two to four hours before taking medicine after eating dairy products


Green leafy vegetables should not be eaten at the same time when taking certain blood-thinning medications.


Bananas, which are high in potassium, should not be taken simultaneously with certain blood pressure-lowering drugs that elevate potassium too.

Fruit juice

It is known that iron should be taken with some orange juice to enhance its absorption. On the other hand, the absorption of certain antihistamines is decreased when given with fruit juice. When a laboratory researcher in Canada took his usual blood pressure-lowering medication in the morning and went to work, he dropped to the floor. His blood pressure was very low. Later on, he remembered drinking two glasses of grapefruit juice along with his medicine.

Grapefruit juice may increase the toxicity of certain high blood pressure reducing medication, cholesterol lowering drugs and immunosuppressants. Pomegranate juice acts in a similar way. Pineapple and cranberry juice are not recommended with blood thinning medication. Cranberry juice, in particular, should be avoided in patients with kidney stones because it is rich in oxalate crystals.

Other foods

Parsley may increase the blood lowering effect of drugs which treat high blood pressure. Its use with aspirin, which we use as a blood-thinning medicine in certain disease conditions in children, may cause a parsley allergy

Liquorice can interfere with blood pressure medications and reduce their effectiveness. It may increase the effect of certain immunosuppressants used in a variety of conditions ranging from kidney diseases to rheumatological disorders

Dark chocolate may interfere with certain Attention Deficit Hyperactivity Disorder medication (ADHD)

Green tea can decrease the absorption of iron. One must not forget that people with a weak liver should limit green tea to two glasses per week because it is toxic to the liver. Of course, one should keep in mind that tea is not recommended for children

Ginger may increase the absorption of alloral medications

Other important interactions

Some foods interfere with the work of the thyroid gland by blocking its utilisation of iodine which is the building block for its hormones. Thyroid hormones should not be taken with calcium-containing foods such as dairy products, dietary fibre, walnuts and fortified juices. They should be taken two hours before or four hours after the foods mentioned above. Also, salty foods should be avoided in patients with high blood pressure or heart disease.

Takeaway tips

Drinking a large glass of water with medicines

Always asking your paediatrician or pharmacist if a particular medicine should be taken with or without food

Reading warnings on the insert in the package

Not mixing medicine into hot drinks

Avoiding giving vitamins to your child at the same time as medicine