5 Foods That Interfere With Medication


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Some oral medications have their absorption modified by interactions with common foods. The latter can slow down, speed up or increase the action of the active ingredients and cause undesirable effects.

Interactions between drugs or between alcohol and drugs are well known to practitioners and are mentioned on the package insert. However, some very common foods can also strongly influence the metabolism of oral medications, leading to an increase in their undesirable effects or, on the contrary, inhibiting their action. When prescribing a drug, ask your doctor or pharmacist for details and they will advise you on how to adapt the treatment.

Interaction between grapefruit and drugs

Some substances in grapefruit inhibit an enzyme that metabolizes certain drugs, which increases their intestinal absorption, with an effect equivalent to an overdose. In other cases, grapefruit instead blocks the absorption of the drug, reducing its effectiveness.

Drugs concerned :

  • statins (cholesterol): simvastatin (whose effect can be multiplied by 15), atorvastatin, lovastatin ;
  • nifedipine(high blood pressure) ;
  • amiodaron (heart rhythm disorders) ;
  • cortison ;
  • fexofenadin (antihistamine);
  • ciclosporin (immunosuppressant).

Bitter oranges can have the same effect, but sweet oranges such as Navel or Valencia are not affected.

The interaction between dairy products and drugs

Calcium-rich foods decrease the digestive absorption of antibiotics such as ciprofloxacin or norfloxacin, as well as osteoporosis drugs (biphosphonates). Dairy products should therefore be consumed at least one or two hours after taking the medication. There is also a risk of hypercalcemia with certain diuretics (hydrochlorothiazide) that decrease urinary calcium elimination.

Interaction between caffeinated drinks and drugs

Antibiotics such as enoxacin, ciprofloxacin and norfloxacin, used in particular to treat urinary tract infections (cystitis) reduce the elimination of caffeine and can therefore lead to an overdose and an increase in side effects (excitement, tremors, palpitations…). Theophylline, an anti-asthmatic, has the same undesirable effects of caffeine which are therefore added to it. It is therefore advisable to avoid coffee, tea, soda or energy drinks containing caffeine during the treatment.

The interaction between licorice and drugs

Consumed in too large quantities, licorice causes cardiac arrhythmia, muscular fatigue and high blood pressure. Moreover, the glycyrrhizic acid contained in the root of the plant affects enzymes of the liver metabolizing drugs, leading to a slowing down or an increase of their absorption.

Drugs concerned:

  • digitalin (cardiac insufficiency) ;
  • diuretics;
  • corticosteroids;
  • oral contraceptives (the steroids it contains have an action similar to that of estrogens.
  • Foods rich in vitamin K
  • Vitamin K is involved in the synthesis and activation of certain plasma coagulation proteins. Consequently, it decreases the effectiveness of anticoagulant drugs such as warfarin, which increases the risk of thrombosis. The ANSM advises not to eat more than one portion per day of foods that contain a lot of it (cabbage, broccoli, spinach, avocado, parsley, lettuce, offal…) and specially to avoid any sudden change in eating habits.