Herb & supplement monograph

Fasting Drug Interactions, Uses, Effectiveness, Safety & More

Medically reviewed by Dr. Brian Staiger, PharmD, BCPS ·Updated July 2026

What is this page for?

First and foremost: how Fasting interacts with medications. The heart of this page is the interaction list — every drug Fasting is known to interact with, and how serious each one is.

But these pages have grown well beyond that into a full monograph — what Fasting is, what people use it for and how strong the evidence is, its safety and side effects, and answers to the questions we’re asked most — written and reviewed by the clinical staff at HelloPharmacist. It’s educational information from our licensed clinical databases, not medical advice, and we don’t sell or endorse products. Our editorial policy

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Interaction report

Drugs that interact with Fasting

208 medications have a known interaction with Fasting, graded by severity. Select any drug for the full evidence-based detail.

2 major interactions. These combinations can be clinically significant — best avoided, or used only with close professional supervision. Always check with your pharmacist before combining them with Fasting.

Don’t want to scroll the list? Just ask.

Tell us the medications you take and we’ll check each one against Fasting using our pharmacist-reviewed interaction data.

AI summaries are generated from our Fasting interaction data for education only — always confirm with your pharmacist. How we use AI

2,830 drugs

Read The List Like a Pharmacist

What Severity, Likelihood & Evidence Mean

Severity — How Serious It Can Be

Major. Clinically significant; generally best avoided, or used only under direct professional supervision.
Moderate. May need monitoring, a dose adjustment, or separating the times you take each one.
Minor. Generally not clinically significant, but still worth noting and mentioning to your pharmacist.
No known interaction. Checked against our sources with nothing documented — not the same as proven safety.

Likelihood — How Well It’s Documented

Likely. Well-controlled human studies have demonstrated the likely existence of this interaction
Probable. Interaction has not been documented in well-controlled studies, however, the interaction has been demonstrated in some small human studies or in controlled animal studies in conjunction with multiple case reports.
Possible. Interaction has been documented in animal or in lab research, or the interaction has been documented in humans but is limited to case reports or conflicting clinical research exists
Unlikely. Interaction has been demonstrated in animal or in lab research but has been shown not to occur in humans.

Where This Data Comes From

Interaction records are evidence-graded and sourced from the Natural Medicines database (TRC Healthcare), the same reference used by pharmacists and hospitals.
Each drug listed above links to the full report for that exact Fasting combination — clinical detail, likelihood, evidence level, and citations.
Content is reviewed by licensed HelloPharmacist pharmacists — see our data sources and editorial standards.

The big picture

The kinds of drugs Fasting affects

Every type of medication (drug category) Fasting is known to interact with. Open any category for the detail — or search your exact drug in the checker above.

All 4 drug categories Fasting interacts with

Warfarin (coumadin)Anticoagulant/antiplatelet DrugsAntidiabetes DrugsInsulin

Warfarin (Coumadin)

Theoretically, fasting may increase the risk of bleeding if used with warfarin.
Both postoperative fasting and Ramadan fasting have been found to increase the INR in patients previously stabilized on warfarin. Closely monitor patients who are fasting while taking warfarin. Dose adjustment may be necessary.

Likelihood Probable Evidence D

Anticoagulant/Antiplatelet Drugs

Fasting may increase the risk of bleeding if used with anticoagulant or antiplatelet drugs.
Fasting has been found to increase the international normalized ratio (INR) in patients stabilized on warfarin. Closely monitor patients who are fasting while taking anticoagulant or antiplatelet drugs. Dose adjustment may be necessary.

Likelihood Possible Evidence D

Antidiabetes Drugs

Fasting might increase the risk of hypoglycemia if used with antidiabetes drugs.
Hypoglycemic events have been reported during intermittent fasting, including in patients using antidiabetes drugs. The risk of having a hypoglycemic event is largest for patients taking insulin or sulfonylureas. The risk of hypoglycemic events seems to be lower for patients taking other antidiabetes drugs such as glucagon-like peptide-1 receptor agonist (GLP- 1RA), metformin, thiazolidinediones, dipeptidyl peptidase-4 inhibitors (DPP4 inhibitors), and sodium-glucose cotransporter-2 (SGLT2) inhibitors. Advise patients to monitor glucose levels closely. Dose or time adjustments may be necessary.

Likelihood Possible Evidence B

Insulin

Fasting might increase the risk of hypoglycemia if used with insulin.
Hypoglycemic events have been reported during intermittent fasting. The risk of a hypoglycemic event seems to be highest in patients using insulin or sulfonylureas. Patients with type 2 diabetes and other comorbidities, or those with type 1 diabetes, should be strongly advised to avoid fasting while taking insulin. For patients taking insulin who insist on fasting, advise these patients to monitor glucose levels closely. Dose or time adjustments may be necessary.

Likelihood Probable Evidence B

Monograph

Fasting: Uses, Safety & Side Effects

Medically reviewed by Dr. Brian Staiger, PharmD, BCPS · Reviewed July 2026 ·

The bottom line

Fasting means voluntarily going without food (and sometimes drink) for set periods. Some research suggests it may help with weight loss and blood sugar in certain people, but results vary and quality of evidence is mixed. It is not safe for everyone, so check with your doctor or pharmacist before starting—especially if you take medication or have a health condition.

Part used: Not applicable (a dietary practice, not a substance)
Common forms: Time-restricted eating, alternate-day fasting, periodic multi-day fasts, intermittent fasting (e.g., 16:8 or 5:2), religious fasting

People commonly use it for

Weight loss
Blood sugar control
Heart health
Religious or spiritual practice
General wellness and longevity

Popular and traditional uses — not proof it works. See “Uses & effectiveness” below for the evidence.

Safety at a glance

OverallUse caution

Often tolerated by healthy adults but can be risky for some people and medications.

PregnancyInsufficient reliable information

There is insufficient reliable information about the safety of intermittent fasting during pregnancy. While there is some evidence that fasting during...

Read the full pregnancy detail

BreastfeedingInsufficient reliable information

Insufficient available evidence; avoid using.

Read the full breastfeeding detail

Pregnancy & breastfeeding ratings are from Natural Medicines (Therapeutic Research Center). Safety guidance is general; always confirm with your pharmacist or doctor for your situation.

Jump to a section

Overview

Fasting is the practice of going without food—and sometimes drink—for a set period of time. Unlike a supplement or herb, it is not a substance you take. Instead, it is a pattern of eating (or not eating) that people follow for health, weight, or spiritual reasons.

Fasting has been part of human life for thousands of years, often tied to religious traditions such as Ramadan, Lent, and Yom Kippur. In recent years, it has also become popular as a wellness and weight-loss strategy.

There are many styles. Intermittent fasting includes patterns like eating only within an 8-hour window each day (often called 16:8) or eating very little on two days a week (the 5:2 plan). Alternate-day fasting rotates between normal eating days and very low-calorie days. Periodic fasting involves going without food for a full day or longer.

How it works

When you go without food for a while, your body shifts how it makes energy. After your stored sugar (glycogen) runs low, the body begins to burn more fat and may produce ketones for fuel—a state sometimes called metabolic switching.

Fasting may also lower insulin levels, give the digestive system a rest, and trigger a cell cleanup process called autophagy, where cells recycle damaged parts. Researchers believe these changes might explain some of the proposed benefits.

It's important to know that many of these mechanisms are based on laboratory and animal studies. How strongly they apply to everyday people, and over the long term, is still being studied.

Effectiveness

Does Fasting work?

Here’s what the research actually shows for each use — graded by Natural Medicines and reviewed by Dr. Brian Staiger, PharmD.

Evidence overview · 29 uses evaluated

3 Possibly effective 26 Insufficient evidence

How to read these evidence grades

Natural Medicines’ 7-point scale. We show each rating’s label word-for-word.

1EffectiveStrong, consistent evidence it works.

2Likely EffectiveGood evidence, though not yet conclusive.

3Possibly EffectiveSome evidence suggests a benefit.

4Possibly IneffectiveSome evidence it may not help.

5Likely IneffectiveFairly strong evidence it doesn’t help.

6IneffectiveStrong evidence it doesn’t work.

7Insufficient Reliable Evidence to RateToo little research to say either way.

Possibly Effective Metabolic syndrome