Can You Fast While Taking Medication?

Intermittent Fasting and Medication

Intermittent fasting is gaining some serious momentum. 36% of Americans say they’ve tried it for weight loss and its other purported health benefits. Have you tried it? 

Research shows a link between intermittent fasting and weight loss, heart health, and insulin sensitivity. However, as with any new eating pattern, you must consider the big picture before you decide if it’s right for you. There is more than one intermittent fasting plan. Take our quiz and figure out what fasting plan could work best for your needs and your lifestyle.

If you take prescription medications, over-the-counter drugs, or supplements, learn how intermittent fasting could adversely impact these substances’ absorption or side effects.

How Fasting May Impact Your Medication Regimen

There are many ways that fasting may affect your medication and supplement routine: 

  • It may increase or decrease the effectiveness of your medications or supplements by inhibiting or enhancing absorption.
  • Fasting may exacerbate the side effects of certain medications and supplements. For example, a common side effect of drugs may be nausea and bloating, which you can typically prevent through food intake.

Fasting and Supplements 

First, let’s talk about your supplements.

Fasting and Fat-Soluble Vitamins 

Vitamins A, D, E, and K are fat-soluble vitamins. You absorb them best when they are taken with a source of fat. Depending on where you live, Vitamin D is an essential daily supplement over the dark winter months. It’s linked to an improved immune system, mood, energy, and respiratory health. Vitamin E is another fat-soluble vitamin that acts as an antioxidant, protecting your cells by fighting free radical damage. If you take Vitamins D and E, or a multivitamin that includes D, take them during your eating window, preferably with a meal containing healthy fat like avocado, olive oil, nuts, seeds, fish, or red meat!

Fasting and Iron Supplements

If you take an iron supplement, fasting may decrease your tolerance to its potential side effects. Iron can cause upset your digestive system and cause cramps and constipation. 

Take your iron supplements with food to help alleviate digestive issues. If iron makes you constipated, try a tablespoon of mineral oil daily. Your body doesn’t absorb mineral oil, so it will help you be regular.

Experiment with timing and see what works best for you. Calcium inhibits iron absorption, so make sure you take iron with non-calcium rich food. In other words, avoid taking your iron supplement with dairy products or milk alternatives. Citrus fruits are your best bet to maximize iron absorption while preventing tummy troubles! 

Intermittent Fasting and Medications 

Diabetes Medications

If you live with diabetes or have challenges managing your blood sugar, speak to your doctor before trying intermittent fasting, especially if you take medications like Metformin or insulin. If you take Metformin on an empty stomach, you could get diarrhea or uncomfortable gas. 

can i take diabetes medication while intermittent fasting

If you take diabetes medication during your fast, you could increase your hypoglycemia risk; a severe low-blood sugar condition. Hypoglycemia can trigger your “fight or flight” response, which can cause fatigue, dizziness, anxiety, and a thumping heart. If your blood sugar remains low, you could get seizures or a more severe condition, so talk to your doctor to adjust your medication.

Thyroid Medication

Levothyroxine is a common medication used to treat hypothyroidism, also known as an underactive thyroid. It’s a human-made version of thyroxine, the primary hormone that’s released by your thyroid gland. You must carefully consider the timing of this medication. One study indicates that thyroxine absorption is 80% in a fasted state, decreasing to 60% in a fed state. Most health care providers recommend taking levothyroxine 30 minutes to one hour before breakfast – this seems to be the sweet spot for most people. However, this study of 90 patients found levothyroxine on an empty stomach before bedtime improved thyroid hormone levels. The best advice? Work with your doctor to find optimal medication timing for your lifestyle. Regardless of timing, the goal is to achieve consistency throughout the week to avoid thyroid level fluctuations. 

Over-the-Counter Medications

Do you ever reach for an aspirin when you pull a muscle, have a tension headache, or when it’s that time of the month? How about ibuprofen or naproxen? These all fall into the category of over-the-counter NSAIDs (Nonsteroidal anti-inflammatory drugs). There’s a consensus that NSAIDs should be taken with some food or a glass of milk to minimize side effects like stomach pain, heartburn, nausea, diarrhea, and constipation. As such, it’s best to take over-the-counter medications during your eating window. Always check the bottle and follow the instructions.

Foods That May Interact With Medications 

There are specific nutrients that may cause an adverse interaction with particular drugs. 

medication on intermittent fasting

Grapefruits interact with some statins, which are medications used to lower LDL-cholesterol. They contain a chemical that can interfere with your body’s ability to break down the statin, leading to an increased level in the blood and possible side effects like rhabdomyolysis. Lovastatin (Mevacor) and Simvastatin (Zocor) seem to be the only drugs for which this is an issue. Typically, it’s only problematic if you eat large amounts of grapefruit. Always talk to your doctor or pharmacist about potential drug/nutrient interactions. 

Grapefruit can also interact with calcium-channel blockers, used for treating high blood pressure and heart disease through the same mechanism of inhibiting breakdown and increasing blood levels of the medication. The increase in blood levels can intensify common side effects like dizziness, constipation, and lower limbs’ swelling. 

So Does Taking Medication Break Intermittent Fasting?

It’s common for gummy multivitamins to contain small amounts of sugar. Sugar triggers an insulin response, which will break your fast. Take your gummy multivitamins in your eating window, preferably with food, to increase absorption of those fat-soluble vitamins. 

So should you fast while taking medications? It depends. Stick with your medication and supplement routine as prescribed. Always talk to your doctor and pharmacist, and double-check your medication instructions before you take them. 

Author's bio


Trista Chan, RD, MHSc

Trista is a Registered Dietitian with her Master of Health Science in Nutrition Communication at Ryerson University, Toronto, and holds an Applied Human Nutrition degree and a graduate certificate in Workplace Wellness. Trista has diverse work experience in organizations both big and small. ...