- GLP-1 medications reduce appetite and food intake, which can lower intake of protein and other nutrients; expert groups point to resistance training and an appropriate diet to help preserve muscle1
- How much protein is right depends on your size, kidney health and other conditions. One 2026 review proposed at least 1.2 g/kg a day (up to 1.6 g/kg in adults without chronic kidney disease), but this is a proposal, not a trial result2; ask your clinician or dietitian for a target
- Stomach and bowel side effects such as nausea, constipation and diarrhea are very common on GLP-1 medications, reported by roughly half or more of users in weight-loss trials3. Probiotics, fiber and magnesium are sometimes used for them, but we did not find trials in people taking GLP-1 medicines, so tell your prescriber about persistent symptoms
- Eating less can lower intake of micronutrients such as iron, vitamin B12, vitamin D, calcium, magnesium and zinc, although most abnormalities reported so far are subclinical or indirect4; a multivitamin may help cover small gaps, but we did not find studies of multivitamins in people taking GLP-1 medicines
- Ask your prescriber or pharmacist before adding any supplement, especially anything that affects blood sugar, and never start, stop, delay or change a prescribed medicine because of this article
GLP-1 Medications and the Nutrition Gap
GLP-1 receptor agonists — semaglutide (Ozempic, Wegovy), tirzepatide (Mounjaro, Zepbound) — have become some of the most widely discussed medications in weight management. In the STEP 1 trial, semaglutide 2.4 mg produced a mean body weight reduction of 14.9% over 68 weeks, compared with 2.4% on placebo.5 In the SURMOUNT-1 trial, tirzepatide produced mean reductions of 15.0% to 20.9% at 72 weeks, compared with 3.1% on placebo.6
These medications act on GLP-1 receptors (tirzepatide also acts on GIP receptors) to reduce appetite, slow gastric emptying and increase feelings of fullness. In a 12-week trial of semaglutide 1.0 mg in 30 adults with obesity, total energy intake across a day of ad libitum meals was 24% lower than on placebo.7 Eating less can also mean lower intake of protein, vitamins, minerals and fiber, particularly if meals are not planned with this in mind.1,8
Weight loss on GLP-1 medicines includes some loss of lean mass as well as fat. A 2026 systematic review of 35 studies found that, in the incretin groups, the median share of total weight loss attributable to reductions in muscle-based measures was 28.3% (interquartile range 15.9% to 39.9%), and no study reported objective physical function outcomes.9 In a SURMOUNT-1 substudy of 160 people measured by DXA scan, about 75% of the weight lost was fat and 25% lean mass, for both tirzepatide and placebo.10 Lean mass on a scan is not the same as muscle, and lean tissue loss does not necessarily indicate weaker strength or physical performance.11 The long-term health effects are not yet known.
This article looks at supplements that people on GLP-1 therapy often ask about, and what the evidence does and does not show for each. Expert groups note that direct evidence on how best to address nutritional gaps in people taking GLP-1 medicines is limited.8 It is not a recommendation to take any supplement. No prescribed medicine should be started, stopped, delayed or changed because of this article; ask your prescriber or pharmacist, particularly if you take other medicines, have kidney disease, diabetes or thyroid disease, are pregnant or breastfeeding, or are considering a supplement for a child.
Protein: Getting Enough While Eating Less
Why Protein Matters During Weight Loss
When food intake falls a lot, some of the weight lost can be lean tissue as well as fat. Expert groups name preserving muscle mass, through resistance training and an appropriate diet, as a priority during GLP-1 treatment.1
Whether preserving lean mass during GLP-1 treatment changes long-term outcomes has not been shown: a 2026 systematic review found that no study reported objective physical function outcomes.9
How Much Protein Does the Research Support?
How much protein is right depends on your size, kidney health and other conditions, so ask your clinician or a registered dietitian. For context, one 2026 narrative review proposed daily protein intakes of at least 1.2 g/kg of body weight (up to 1.6 g/kg in adults without chronic kidney disease) for people on these medicines. This is a proposal by the review author, not a trial result.2 An expert consensus statement notes that its recommendations are primarily derived from indirect evidence.8
When appetite is low, reaching a protein target from food alone can be harder. In a pooled analysis of three placebo-controlled trials lasting at least four weeks (209 participants), GLP-1-type medicines lowered energy intake at a standardized lunch by about 270 kcal;12 we did not find a reliable figure for typical daily calorie intake on these medicines. Some people use protein powders, shakes or meal replacements for this reason. In calorie-restricted weight-loss trials that did not involve GLP-1 medicines, higher-protein diets modestly mitigated the loss of fat-free mass (by about 0.4 kg in a meta-analysis of 24 trials),13 although a 2026 meta-analysis of 22 trials in adults without kidney disease found no significant effect of high-protein diets on fat-free mass.14 No trial has tested protein supplements specifically in people taking GLP-1 medicines. A 2026 review notes that protein supplements and nutritionally complete meal replacements may be useful when intake is insufficient.11
In adults without kidney disease, the same 2026 meta-analysis found no consistent evidence of kidney injury with high-protein diets, but most trials were short and the long-term kidney effects are uncertain.14 If you have kidney disease, ask your clinician for your protein target before using protein supplements or meal replacements.
Features that some people look for in protein products include:
- Known, consistent protein content per serving (10g, 15g, or 30g depending on format)
- Controlled, modest calorie counts (90–220 calories per serving) that fit within reduced intake
- Easy-to-consume formats (shakes, bars, soups, entrees) that may be easier to manage when appetite is low
- A way to track protein intake against a target set with your clinician or dietitian
Probiotics and Gut Health: What Is and Is Not Known
Understanding GLP-1 and the Digestive Tract
GLP-1 medications slow gastric emptying and the motility of the small intestine,15 which helps limit blood sugar rises after meals and contributes to fullness. The effect lessens with prolonged treatment: in one study of tirzepatide, the delay in gastric emptying was greatest after the first dose and diminished with repeated dosing in healthy participants, with a smaller residual delay in people with type 2 diabetes.16
Gastrointestinal side effects are the most common adverse effects of these medicines. In a 2025 systematic review of 26 placebo-controlled trials in adults without diabetes, gastrointestinal adverse events were reported in 47% to 84% of people on GLP-1 receptor agonists and co-agonists (including some not yet on the market) versus 13% to 63% on placebo, most commonly nausea, vomiting, diarrhea and constipation.3 In the STEP 1 trial, nausea and diarrhea were the most common adverse events with semaglutide, and 4.5% of people on semaglutide stopped treatment because of gastrointestinal events, compared with 0.8% on placebo.5 In SURMOUNT-1, the most common adverse events with tirzepatide were gastrointestinal, occurring primarily during dose escalation, and adverse events caused treatment discontinuation in 4.3% to 7.1% of tirzepatide groups compared with 2.6% on placebo.6 Persistent or severe symptoms should be discussed with your prescriber; do not stop or change your medicine on your own.
GLP-1 medications are also associated with a higher risk of gallstones and gallbladder or biliary disease, particularly in weight-loss trials (relative risk 2.29 across 13 weight-loss trials, versus 1.27 in trials for type 2 diabetes or other diseases), with higher risk at higher doses and with longer use.17 Seek medical care promptly for severe upper-abdominal pain, fever or yellowing of the skin.
What the Research Shows About Probiotics
Studies of gut bacteria during GLP-1 treatment are small. In one 12-week study of 15 adults with type 2 diabetes taking semaglutide, the composition of gut bacteria changed (for example, Bifidobacterium increased and Klebsiella decreased) alongside improvements in blood sugar, body weight and blood lipids. Samples were compared before and after treatment, with no probiotic arm.18 We did not find a trial showing that probiotics change these shifts, or that they improve gut symptoms, in people taking GLP-1 medicines.
In adults with functional constipation (not specific to people taking GLP-1 medicines), a meta-analysis of 15 randomized trials found that probiotics reduced whole gut transit time by 13.75 hours and increased stool frequency by 0.98 bowel movements per week; the increase was significant for multispecies probiotics but not for Bifidobacterium longum alone.19 We did not find trials of prebiotic fiber or probiotics for GLP-1 side effects.
Probiotics are generally considered safe for most people, but serious infections and other effects have been described in susceptible individuals,20 and in a trial of 298 people with predicted severe acute pancreatitis, a multispecies probiotic was associated with higher mortality (16% vs 6%).21 A 2026 meta-analysis found the evidence insufficient to draw conclusions about long-term safety in at-risk groups.22 If you have a weakened immune system, pancreatitis or a serious illness, ask your clinician before taking a probiotic.
Multivitamins and Micronutrient Gaps
Eating much less can lower intake of micronutrients. A 2026 review names iron, vitamin B12, vitamin D, calcium, magnesium and zinc as areas where signals of risk have been reported during GLP-1 treatment, but says most abnormalities seen so far are subclinical or indirect, with clinically meaningful consequences possible in susceptible people, such as those with prolonged nausea and vomiting or a poor-quality diet.4 We did not find evidence that GLP-1 medicines directly deplete a specific vitamin.
Nutrients that the 2026 review and other sources discuss include:
- Vitamin B12 and other B vitamins: B12 comes mainly from animal foods, so eating much less could lower intake; the 2026 review also lists folate and thiamine as context-dependent concerns.4 A blood test is the way to know your level, and a clinician can advise whether a supplement is needed
- Iron: listed among the nutrients with risk signals;4 iron status can be checked with a blood test, and extra iron should be taken only if your clinician advises it
- Vitamin D and calcium: also listed among the nutrients with risk signals.4 A 25-hydroxyvitamin D blood test is the way to know your vitamin D level
- Zinc and magnesium: listed among the nutrients with risk signals,4 and low dietary magnesium intake is common even without GLP-1 medicines (see the magnesium section below)
A daily multivitamin may help cover small gaps when eating less, but it is not a substitute for a varied diet, and we did not find studies of multivitamins in people taking GLP-1 medicines. The 2026 review suggests individualized nutritional assessment and targeted laboratory monitoring for high-risk patients, such as those with prior bariatric surgery, gastrointestinal disorders, poor baseline diet quality or older age.4
Some multivitamins contain vitamin K, which affects warfarin-type blood thinners. In healthy volunteers taking an oral anticoagulant, vitamin K2 (MK-7) at doses as low as 10 mcg a day lowered the INR in some people, and the authors concluded that MK-7 supplements need to be avoided in patients receiving vitamin K antagonist therapy.23 If you take warfarin or a similar medicine, ask your prescriber before using any product that contains vitamin K. In a systematic review, limited evidence suggested that calcium and iron supplements reduce the absorption of levothyroxine, so if you take thyroid hormone, ask your prescriber or pharmacist about timing.24
Omega-3 Fatty Acids
Omega-3 fatty acids (EPA and DHA) are found mainly in fatty fish, so eating less could lower intake, although we did not find studies measuring omega-3 intake in people taking GLP-1 medicines. Whether omega-3 supplements help preserve muscle during weight loss is not established. A small 2011 study in nine healthy adults found that 8 weeks of high-dose omega-3 (4 g/day) increased the muscle's response to an infusion of insulin and amino acids; it did not test calorie restriction or measure lean body mass.25 A 2026 review lists omega-3 fatty acids among adjunctive options in GLP-1 care that are supported mainly by indirect or phenotype-specific evidence.11
Omega-3 dose matters for safety. A 2026 meta-analysis of 35 trials found a higher risk of atrial fibrillation only with EPA and DHA doses above 1,500 mg/day in people at high cardiovascular risk (odds ratio 1.43, 95% CI 1.14 to 1.79; absolute risk difference 0.8%), and not with lower doses.26 A meta-analysis of 11 randomized trials found no overall increase in bleeding with omega-3, but high-dose purified EPA was associated with a 50% higher relative risk of bleeding (0.6% higher absolute risk).27 If you have a heart-rhythm condition or take blood thinners, ask your clinician before taking omega-3.
Separately, in the SELECT trial of 17,604 adults aged 45 or older with established cardiovascular disease and overweight or obesity but without diabetes, semaglutide 2.4 mg reduced the composite of cardiovascular death, nonfatal heart attack or nonfatal stroke (6.5% vs 8.0% on placebo; hazard ratio 0.80, 95% CI 0.72 to 0.90) over a mean follow-up of about 40 months.28 This result concerns the medicine, not omega-3 supplements, and we did not find trials of omega-3 supplements in people taking GLP-1 medicines.
Magnesium
Magnesium is a mineral involved in many processes in the body, including muscle and nerve function and glucose metabolism. In 2005–2006, about 48% of the US population consumed less than the required amount of magnesium from food.29 That is low intake, not a measured deficiency. On a lower-calorie diet, magnesium-rich foods such as whole grains, legumes, leafy greens and nuts may be eaten less, so the gap between intake and need could widen; we did not find studies measuring this in people taking GLP-1 medicines. Muscle cramps, poor sleep and constipation have many possible causes, and we did not find evidence that they are caused by low magnesium in people taking GLP-1 medicines. Discuss persistent symptoms with your prescriber.
Magnesium oxide is poorly absorbed (fractional absorption about 4% in a study of normal volunteers), while magnesium chloride, lactate and aspartate were absorbed significantly better and about equally well.30 Magnesium glycinate was not tested in that study, and we did not find trials showing that it is better absorbed or better tolerated than other forms. Magnesium supplements can cause diarrhea at higher doses.31 A systematic review of three small trials in 151 older adults with insomnia found that magnesium shortened the time to fall asleep by about 17 minutes compared with placebo, but the evidence was of low to very low quality and total sleep time did not change significantly; it has not been tested for sleep in people taking GLP-1 medicines.32 The US upper limit for supplemental magnesium in adults is 350 mg/day of elemental magnesium from supplements alone, based on diarrhea as the limiting effect; a 2023 perspective argues that this limit should be re-evaluated.31 We did not find studies of magnesium for constipation or muscle cramps in people taking GLP-1 medicines. If you have kidney disease, ask your clinician before taking magnesium supplements, and ask your prescriber or pharmacist whether magnesium could interact with your medicines.
A Note on Berberine: Use With Caution
Berberine is a plant compound sold as a supplement for blood sugar and cholesterol, and it is often marketed alongside GLP-1 medicines as "nature's Ozempic".33 It has not been studied together with GLP-1 medicines, and it is not a substitute for them. In trials, berberine lowered blood glucose modestly: a meta-analysis of 20 randomized trials found reductions in fasting glucose of 0.52 mmol/L and in HbA1c of 4.48 mmol/mol (7 studies).34 A meta-analysis of 18 placebo-controlled trials found small reductions in LDL cholesterol and triglycerides, with gastrointestinal side effects reported in 2–23% of berberine groups compared with 2–15% of placebo groups.35
Berberine lowers blood glucose, so it may add to the effect of GLP-1 medicines and metformin. In a meta-analysis of 37 trials in type 2 diabetes it did not significantly raise the risk of hypoglycemia (relative risk 0.48, 95% CI 0.21 to 1.08),36 but it has not been tested with GLP-1 medicines, and additive low blood sugar is listed among its potential drug interactions.33 Berberine can also interact with other medicines (it increased ciclosporin exposure in kidney transplant recipients),33 and a 2026 toxicology review lists pregnancy status among the factors that modify its toxicity, so ask a clinician before using it if you are pregnant or planning pregnancy.37 Talk to your prescriber or pharmacist before starting, especially if blood sugar management is already part of your health picture. This is not a supplement to add casually alongside a GLP-1 medication.
Products to Be Cautious With
Some products have specific concerns when taken alongside GLP-1 medicines. Ask your prescriber or pharmacist before using any of these:
- Stimulant-based fat burners or weight loss supplements: we did not find evidence that they add benefit alongside GLP-1 medicines. In a review of adverse-event reports submitted to the US Food and Drug Administration, caffeine-containing weight-loss and pre-workout products had greater odds of a reported event being life-threatening or fatal than non-caffeinated products; such reports cannot show how often events occur.38
- Energy and pre-workout products with caffeine: in the same review, these had greater odds of the reported event being fatal than non-caffeinated products;38 we did not find studies of caffeine intake in people taking GLP-1 medicines, so ask your prescriber or dietitian if nausea or stomach discomfort is a problem
- Megadose fat-soluble vitamins: vitamins A, D, E and K are fat-soluble, and separate high-dose supplements on top of a multivitamin can add up. For vitamin D, a review states that an upper limit of 4,000 IU/day is consistently accepted for adults and that larger doses over the long term should not be selected.39 Check product labels for total amounts, and do not exceed upper limits without medical advice
- Herbal digestive products with unknown ingredients or stimulant laxative effects: ask your prescriber or pharmacist first, given existing gastrointestinal sensitivity
Medicine absorption. GLP-1 medications slow gastric emptying, which can change how some oral medicines are absorbed. A 2025 review found most of these interactions clinically insignificant, but significant changes in exposure were seen with levothyroxine and oral semaglutide, and with oral contraceptives and tirzepatide.40 In healthy volunteers, oral semaglutide raised total thyroxine exposure by 33% when taken with levothyroxine,41 and in one study a single dose of tirzepatide lowered peak levels of the contraceptive hormones by 55–66% and overall exposure by 20–23%; whether this changes contraceptive effectiveness has not been established.42 If you take thyroid hormone, an oral contraceptive or any other oral medicine, ask your prescriber or pharmacist about timing and whether any extra precautions are needed before adding any supplement. This includes all of the supplements discussed in this article.
Summary of Options
The options below are ones that people on GLP-1 therapy often ask about. This summary is not a protocol or a recommendation, and direct evidence in people taking GLP-1 medicines is limited for all of them.8
- Protein: a target set with your clinician or dietitian; protein shakes or meal replacements are one way some people reach it. Ask first if you have kidney disease
- Multivitamin: may help cover small gaps; follow the product label, and ask first if you take warfarin or another prescription medicine
- Probiotic: not tested for GLP-1 side effects; ask first if you have a weakened immune system, pancreatitis or a serious illness
- Omega-3 (EPA + DHA): lean-mass benefit not established; doses above about 1,500 mg/day were linked to atrial fibrillation in people at high cardiovascular risk, so ask first if you have a heart-rhythm condition or take blood thinners
- Magnesium: supplemental upper limit 350 mg/day of elemental magnesium; ask first if you have kidney disease
This is general information, not a personalized recommendation. Your individual needs depend on your baseline nutritional status, which medications you take, and your health conditions, all of which your prescriber, pharmacist or a registered dietitian is best positioned to assess. No prescribed medicine should be started, stopped, delayed or changed because of this article.
Frequently Asked Questions
Research References
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Medical disclaimer: This article is written for educational purposes by the Kasivit Editorial Team and reflects a review of published research. It does not constitute medical advice and is not a substitute for consultation with your prescribing physician, pharmacist or another qualified healthcare provider. GLP-1 medications are prescription drugs; no prescribed medicine should be started, stopped, delayed or changed on the basis of this article, and any change to your supplement regimen should be discussed with your prescribing team or pharmacist. Supplement information here is general and may not be appropriate for everyone, particularly people with kidney disease, thyroid disease or diabetes, people who are pregnant or breastfeeding, children, and people who take several medicines. These statements have not been evaluated by the Food and Drug Administration. Products mentioned are not intended to diagnose, treat, cure, or prevent any disease.
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