By Helaine Krasner MS, RDN, CDN

Many people are not aware that the safety and effectiveness of certain medications can be impacted not only by when they are taken but what they are taken with. Certain food components can either decrease absorption, thus decreasing effectiveness of a medication, or can affect how easily the body metabolizes and clears the mediation from the system. This can result in high levels of a medication accumulating in the body with potential negative effects.

Some medications can be taken with or without food while others should be taken on an empty stomach. Always pay attention to instructions on how and when to take your medications and if there are certain foods to avoid. Consult with your doctor, pharmacist or dietitian about potential food and drug interactions.

Some common food-drug interactions:

  1. Grapefruit and atorvastatin, lovastatin or simvastatin –inhibits metabolism and increases absorption and plasma concentrations of these cholesterol lowering medications. Signs of toxicity can include headache, stomach upset and muscle pain.1
  2. Grapefruit juice and calcium channel blockers – increases absorption and plasma concentrations of these blood pressure medications. Signs of toxicity can include flushing, headache, tachycardia and hypotension.1
  3. Grapefruit and clopidegrel (Plavix) – decreases plasma levels possibly reducing antiplatelet effects.1
  4. Grapefruit and estrogens – increases levels of endogenous (produced by the body) and exogenous (taken in from outside the body) estrogens.1
  5. Grapefruit and sildenafil (Viagra) – inhibits drug metabolism, increasing absorption and plasma concentrations of this erectile dysfunction medication.1
  6. Dark leafy greens and warfarin (Coumadin) – increases in habitual intake could reduce effectiveness of this anti-clotting medication. Keep consumption of these nutritious foods high in vitamin K (i.e. kale, collards, spinach, Brussels sprouts, broccoli, asparagus) relatively consistent.2 (Contrary to popular belief it is not necessary to eliminate these vegetables from the diet.)
  7. Dairy (calcium-rich foods) and ciprofloxacin and tetracycline – decreases absorption due to binding of calcium to the antibiotics. Don’t take these antibiotics with dairy products.2
  8. Calcium and Levothyroxine (Synthroid) – binds to medication resulting in reduced absorption.1 Take medication in the morning at least 1 hour before eating.3 Take this medication four hours apart from iron, calcium or antacids to avoid decreased absorption.3

An additional note regarding supplements and medications:

Some vitamins and herbal supplements can either increase or decrease the effects of some medications. Discuss proper use with your healthcare provider or pharmacist.

Important things to remember:

Tell your healthcare provider about all medications and supplements you are taking and never take medication with alcohol.



  1. Interaction checker. Natural Medicines Database. Accessed November 22, 2019.
  2. Bareuther C. Dangerous food-drug interactions. Today’s geriatric medicine. 2008; 1(4)
  3. Important safety information. Synthroid website. Accessed November 22, 2019.


Helaine Krasner MS, RDN, CDN is a registered dietitian nutritionist who takes great pride in helping our Bariatric and Medical Weight Management patients achieve their health and weight loss goals.