Fasting and weight-loss medications: what to advise your patients

As the newly licensed Wegovy pill joins injectable GLP-1s on the UK market, primary care pharmacists are increasingly the first point of contact for patients navigating fasting — from Ramadan to dietary intermittent fasting. Advanced dietetic practitioner, Angela Carvalho, sets out how clinicians can advise patients safely and sensitively

Glucagon-like peptide-1 (GLP-1) agonists, such as semaglutide and tirzepatide, and other incretin therapies are now widely used for type 2 diabetes and weight management

IQVIA data show that more than 2.37 million people in the UK were accessing GLP-1s in 2025, with around 90% accessing these privately and only 200,000 receiving them through the NHS.^1,2

Because many private prescribers offer limited follow-up, practice and community pharmacists are often the first, and sometimes only, clinical contact for these patients

Guidance around GLP-1 use is evolving rapidly, including questions around cultural or religious fasting – such as Ramadan, Lent, Yom Kippur and Hindu or Jain fasts – and patient-led intermittent fasting, such as 5:2, 16:8, and time-restricted eating

This article supports primary care pharmacists in offering proactive, individualised advice about GLP-1 medicine use, before a planned fast

Injectable versus oral

Most GLP-1s are given as subcutaneous injections, for example weekly semaglutide or tirzepatide, or daily liraglutide. However, in June 2026 the Medicines and Healthcare products Regulatory Agency (MHRA) approved the first GLP-1 tablet, oral semaglutide, for weight management and as of 6 July the Wegovy pill is now available for sale in the UK.³

Unlike the injectables, the oral GLP-1 tablet only works if taken on an empty stomach. It should be taken once daily, first thing in the morning, having ideally not eaten or drunk anything for at least eight hours beforehand. Patients are also advised to wait at least 30 minutes before eating, drinking anything else, or taking other oral medicines.³

How GLP-1s interact with fasting

All GLP-1 agonists slow gastric emptying, suppress appetite and stimulate glucose-dependent insulin release.⁴ Fasting can amplify these effects, increasing the risk of constipation, dehydration and nutritional deficiencies.⁵

GLP-1-induced weight loss is also accompanied by some reduction in lean body mass, which is clinically relevant in older patients or those with low muscle reserves.⁶ Fasting can compound this – when energy and protein intake fall, the body is more likely to draw from muscle in addition to fat.⁶

Fasting during Ramadan

Ramadan involves abstaining from eating, drinking and oral medications from dawn to dusk during the ninth lunar month.7 Two meals are eaten: Suhoor before dawn and Iftar at sunset

Fasting is considered obligatory for all healthy Muslims who have reached puberty. There are exemptions such as individuals with chronic health conditions (particularly older adults), pregnant women and people with mental health conditions.⁸

Many individuals may still choose to fast, however. Importantly, the role of healthcare professionals is not to dissuade patients but to use a process of shared decision-making to assess the level of risk for the individual and to provide advice tailored to their medical needs

Similar principles apply to other faith-based fasts, though patterns and rules on fluids vary

Advice on GLP-1 use when fasting

Avoid dose escalation in the run-up to a fast

The International Diabetes Federation and Diabetes and Ramadan (IDF-DAR) and the Southeast London Area Prescribing Committee recommend completing dose titration at least four to six weeks before Ramadan, so that gastrointestinal side effects have time to settle.9,10 Defer dose escalation if fasting begins imminently

Should GLP-1s be continued?

Any pause and restart of GLP-1s should be planned

Patients who stop treatment altogether risk regaining around two-thirds of the weight they’ve lost after roughly a year off the medicine, with cardiometabolic markers returning towards baseline in the same period.¹²

However, this is not what happens after a short, planned pause of a few weeks during Ramadan or other short-term fasts – the concern is sustained discontinuation

Importantly, resuming at the previous dose after any break may also bring back stronger side effects

For injectable GLP-1s, IDF-DAR 2021 guidance supports safe continuation in type 2 diabetes for patients on stable therapy and this does not invalidate the Islamic fast.^9,11 Oral GLP-1s are different because a swallowed tablet reaches the stomach, so if taken during fasting hours would break the fast.^9,11

Evidence of using GLP-1s for weight management during Ramadan is limited at present; however, there is existing evidence supporting the safe and effective continuation of GLP-1s in diabetic patients.5 Patients may wish to confirm with their religious advisor

Patients at high risk – such as those co-prescribed insulin or sulfonylureas, those with recent severe hypoglycaemia, pregnancy or those who have had recent diabetic ketoacidosis – should be advised that fasting may be unsafe.⁹

Weekly injectable GLP-1s should be taken on the same day each week and daily injections should be taken at the same time each day. Injecting after Iftar may minimise nausea; injecting after Suhoor may help satiety through the day. Avoid changing both day and dose together

The GLP-1 tablet must be fitted into the overnight eating window, ideally on waking for Suhoor, on an empty stomach with the permitted sip of water, then to wait 30 minutes before eating Suhoor. Patients for whom the timing is too tight may be better suited to an injectable GLP-1 during Ramadan, or to a planned pause, but this is an individualised decision

Healthy eating and hydration during Ramadan

Suhoor: high-fibre starchy foods (brown rice, oats, bulgur wheat) give slow-release energy; pulses add protein and satiety; fruit and vegetables help prevent constipation. Keep portions moderate and limit high-fat, high-sugar and spicy foods. It is important to drink enough sugar-free and decaffeinated fluids to avoid dehydration during the day

Iftar: dates are traditional to break the fast and are high in fibre, but consumption should be limited to one or two as they are also a rich to rehydrate, and limit caffeine, sweet treats and fried foods

For GLP-1 specific dietary advice, patients can be signposted to the British Dietetic Association’s Guide to eating and living well while taking medications for obesity re

Intermittent fasting

Some patients ask about combining GLP-1s with intermittent fasting, and it is worth having an informed discussion

The common fasting patterns are time-restricted eating such as 16:8, which is eating within an eight-hour window each day and fasting for the other 16 hours, and the 5:2 diet, involves eating normally for five days and markedly restricting intake – typically to around 500-600kcal – on two non-consecutive days

Systematic review evidence shows intermittent fasting produces weight loss broadly equivalent to continuous calorie restriction, rather than superior to it.14 In patients on a GLP-1, which already substantially reduces appetite and intake, the question is whether adding fasting on top offers added benefit and can be sustained without compromising nutritional adequacy. Unfortunately, there is currently insufficient evidence to definitively answer this

Ideally patients should not skip meals while on GLP-1s. However, for those who wish to try intermittent fasting while on a GLP-1, the priority is meeting daily protein and micronutrient needs within a reduced eating window and staying well hydrated

Patients should also prioritise regular resistance activity to preserve muscle and should speak to a registered dietitian for tailored advice on this

Many people who already intermittent fast start a GLP-1 to reduce intrusive thoughts around food or ‘food noise’. Importantly, intermittent fasting is not appropriate for those with a history of disordered eating, since restrictive patterns can worsen their relationship with food

As with any dietary pattern, the goal is sustainable, balanced intake rather than adherence to a specific regimen

Side effects and when to escalate

Fasting can magnify common GLP-1 side effects, and some presentations may need urgent referral. Intercurrent illness, such as a vomiting bug or fever, is itself a reason to advise breaking the fast

Hypoglycaemia

Low risk for people with diabeteson monotherapy but rises with co-prescribed insulin or sulphonylureas. If experiencing a hypoglycaemic episode, patients should break the fast immediately and take fast-acting carbohydrate. Islamic guidance permits this.⁵

Nausea and vomiting

Advise small, frequent meals; avoid spicy, fried or strong-smelling foods and lying flat after eating. Persistent vomiting beyond 24 hours or dehydration warrants review and consideration of pausing the dose

Constipation

Encourage wholegrains, pulses, fruit and vegetables, fluids and light activity

Dehydration and acute kidney injury

Refer urgently if reduced urine output, postural symptoms (dizziness on standing) or marked fatigue; check urea and electrolytes if clinically indicated

Other red flags

Persistent severe abdominal pain (consider pancreatitis), and symptoms of ketosis or diabetic ketoacidosis in people with diabetes (such as excessive thirst, frequent urination, nausea and vomiting, abdominal pain, fruity-smelling breath, and drowsiness or confusion) require urgent referral

Where there is recurrent hypoglycaemia, severe gastrointestinal intolerance or pregnancy, suggest pausing the fast rather than the medication

Sensitively remind patients that obesity and many co-morbidities are recognised grounds for religious exemption

Key takeaways

• Ask all GLP-1 patients about planned fasting at every review.
• Complete dose titration at least four to six weeks before any planned fast.
• For injectables, keep timing consistent and adjust to suit the individual.
• For the oral tablet, take on an empty stomach and fit it into their eating window rather than the fast.
• Prioritise balanced meals with protein and fibre, and adequate hydration.
• Highlight circumstances in which breaking the fast is appropriate and reassure patients that this can be clinically and religiously legitimate.

Angela Carvalho, Advanced Dietetic Practitioner & Non-Medical Prescriber, NHS Lothian, Edinburgh

Competing interests:Private dietetic practice, contribution to clinical trials involving GLP-1 therapies as part of NHS role (Boehringer Ingelheim, Eli Lilly), contribution to Scottish Government GLP-1 guidance and acted as clinical expert advisor to the Scottish Medicines Consortium, Scotland Representative for the BDA Obesity Specialist Group which includes involvement in oversight of GLP-1 resources

Resources

References

1. IQVIA. Written evidence submitted to the UK Parliament Health and Social Care Committee (FWM0029). https://committees.parliament.uk/writtenevidence/146947/pdf/
2. Jackson SE, et al. Prevalence of use and interest in using glucagon-like peptide-1 receptor agonists for weight loss: a population study in Great Britain. BMC Med 2026;24:1.
3. Medicines and Healthcare products Regulatory Agency. First GLP-1 tablet for weight loss approved in the UK. https://www.gov.uk/government/news/first-glp-1-tablet-for-weight-loss-approved-in-the-uk
4. Drucker DJ. Mechanisms of action and therapeutic application of glucagon-like peptide-1. Cell Metab 2018; 27: 740–756.
5. Alayed KM. Glucagon-like peptide-1 (GLP-1) during Ramadan: narrative review of the published literature. J Obes 2023; 2023: 8626081.
6. Sandsdal RM, et al. Combination of exercise and GLP-1 receptor agonist treatment reduces severity of metabolic syndrome, abdominal obesity, and inflammation: a randomized controlled trial. Cardiovasc Diabetol 2023; 22: 41.
7. Ahmed MH, Abdu TA. Diabetes and Ramadan: an update on the use of glycemic therapies during fasting. Ann Saudi Med 2011; 31: 402–406.
8. Ahmed S, et al. Fasting during Ramadan: a comprehensive review for primary care providers. Diabetology 2022; 3: 276–291.
9. Hassanein M, et al. Diabetes and Ramadan: practical guidelines 2021 (IDF-DAR). Diabetes Res Clin Pract 2022; 185: 109185.
10. NHS South East London Area Prescribing Committee. Clinical guidance for the management of diabetes in Ramadan for healthcare professionals in primary care. https://www.selondonics.org
11. International Islamic Fiqh Academy. Invalidators of fasting in medical treatments. https://iifa-aifi.org/en/32535.html
12. Wilding JPH, et al. Weight regain and cardiometabolic effects after withdrawal of semaglutide: the STEP 1 trial extension. Diabetes Obes Metab 2022; 24: 1553–1564.
13. British Dietetic Association. Medications for obesity: a guide to eating and living well while taking medications for obesity. https://www.bda.uk.com/food-health/glp-1-obesity-medications.html
14. Cioffi I, et al. Intermittent versus continuous energy restriction on weight loss and cardiometabolic outcomes: a systematic review and meta-analysis of randomized controlled trials. J Transl Med 2018;16:371.

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