Millions of people worldwide – as many as 1 in 8 adults in the U.S. – are on GLP-1 medication, such as Ozempic, Mounjaro, Wegovy and Zepbound, for treating diabetes or for weight loss.

These drugs are adding a medical twist to religious observances that involve fasting, such as the Jewish holiday of Yom Kippur, which will be observed from sundown on Sept. 20 until nightfall on Sept. 21, 2026. Traditionally, fasting on Yom Kippur means forgoing food and water for about 25 hours, which can strongly affect a person’s metabolism.

Other religious traditions include different types of fasts. For example, Muslims who fast during Ramadan neither eat nor drink from dawn to sunset, but they break their fast each night. Christian and Hindu traditions also include dry fasts as well as partial fasts, such as Lent and Navratri, in which people avoid certain foods.

As a specialist in obesity medicine, I work with many patients who take GLP-1 drugs. Most people can safely fast for Yom Kippur or other religious or cultural observances. But depending on their circumstances, they may need to plan ahead, take certain precautions and be clear on when it’s medically advised that they break their fast.

Common GLP-1 side effects and fasting

GLP-1 drugs such as Ozempic, Mounjaro, Wegovy and Zepbound mimic a natural gut hormone– glucagon-like peptide 1 – that lowers your blood sugar by triggering insulin release when your blood sugar is high. These drugs also slow how quickly food passes through the stomach, which reduces appetite to aid in weight loss.

GLP-1s have some common side effects that can occur in anyone taking them, including nausea, vomiting, dizziness, constipation and dehydration. Fasting may exacerbate them, especially in people who are prone to an upset stomach. GLP-1 side effects are also more common when a patient is increasing their dose, which usually happens monthly as tolerated until they reach their full dosage.

That’s why, if you’re planning to fast for Yom Kippur, it’s best to avoid starting a new GLP-1 medication or increasing the dose of your medication sooner than two weeks or so before the holiday.

If you take GLP-1 drugs as weekly injections, which is the most common way of dosing these medications, you should stick to your schedule even if you plan to fast. These drugs stay in your system during the........

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