Walk into any GLP-1 forum and you'll find long lists of supplements people swear by. It's easy to come away thinking you need a shelf full of bottles to do this right. You don't. For most people, no supplement is required to lose weight or to take a GLP-1 medication safely.
There is a real reason supplements come up so often on these drugs, though, and it's worth understanding.
Why the calorie deficit changes the math
GLP-1 medications work largely by turning your appetite down. The catch is that eating less food also means taking in less of everything that comes packaged in food: protein, fiber, vitamins, minerals. At 2,200 calories a day, hitting your nutrition targets was easy. At 1,300 calories with a smaller appetite, the same targets are hard to reach from food alone.
Supplements don't do the weight loss, and they can't fix a poor diet. They're insurance: a way to close specific gaps that a calorie deficit tends to open. If you eat well-planned, protein-forward, produce-heavy meals, you may need almost nothing. If you're struggling to eat much of anything on a high dose, a few targeted additions may help.
Food first, always. Whole foods deliver nutrients in forms and combinations a pill can't copy, plus fiber, water, and fullness. Use supplements for the gaps you can't close at the table.
The supplements people on GLP-1s commonly take
They're listed roughly in order of how useful and well-supported they are. Each one ends with a short read on the strength of the research: some are solid, some are reasonable but thin.
Protein powder (whey, casein, or plant)
This is the big one. Protein protects muscle during weight loss and keeps you fuller, but it's the hardest target to hit on a small appetite. A scoop can add 20–30 g without much volume, which helps when a chicken breast feels like too much (more ideas for eating protein on a low appetite).
Guidance during weight loss often lands around 1.2–1.6 g of protein per kg of body weight per day, spread across meals. A review in the American Journal of Clinical Nutrition found that higher-protein diets help preserve lean mass and increase satiety, though longer-term results depend on people sticking with them (Leidy et al., 2015, DOI (external link)). Powder is just a convenient way to get there when food won't. Evidence: moderate for the protein itself; the powder is only a convenience.
Fiber (psyllium and others)
Constipation is one of the most common GLP-1 side effects. Digestion slows, you eat less, and you often get less fiber. A fiber supplement can help keep things moving.
Psyllium is a soluble fiber. In a randomized trial of people with chronic constipation, it softened stool and worked better than the stool softener docusate (McRorie et al., Alimentary Pharmacology & Therapeutics, 1998, DOI (external link)). Add it gradually and with plenty of water, or it can backfire. Evidence: strong for constipation relief. Our full fiber guide covers types, targets, and powder vs. capsules.
Creatine
Creatine is increasingly popular with people doing resistance training to protect and build muscle while losing fat. It's cheap, well studied, and one of the few sports supplements that reliably does something.
In a meta-analysis of older adults, creatine plus resistance training produced about 1.4 kg more lean tissue mass than training alone, along with greater strength gains (Chilibeck et al., Open Access Journal of Sports Medicine, 2017, DOI (external link)). Those trials paired it with training, and that's how to use it. Evidence: strong when paired with strength work.
Collagen peptides
No supplement is marketed harder to this audience, for loose skin, hair, and aching joints, and none is more often misunderstood.
The evidence is mixed. Meta-analyses find improvements in skin hydration and elasticity, but the largest analysis to split trials by funding source found no effect in non-industry-funded or high-quality trials (Myung & Park, The American Journal of Medicine, 2025, DOI (external link)). Joint evidence is somewhat stronger than skin evidence: in a network meta-analysis of supplements for knee osteoarthritis, collagen helped on some outcomes, though Boswellia ranked highest for pain and stiffness (Zhang et al., Nutrients, 2025, DOI (external link)). Tendon evidence is unsettled.
The important caution: collagen is low in essential amino acids and contains no tryptophan, so it should never replace part of your protein target. Add it on top. Our full collagen guide explains what the Type I/II/III labels mean and grades each claim separately. Evidence: modest and mixed, and collagen is no protein substitute.
Vitamin D and calcium
Weight loss, especially a sustained calorie deficit, can reduce bone density. A review of calorie-restricted diets found lower bone mineral density and recommended getting enough calcium and vitamin D, from food or supplements, to protect bone during weight loss (Veronese & Reginster, Aging Clinical and Experimental Research, 2019, DOI (external link)). Many people also start out short: in U.S. survey data, adults eligible for GLP-1 obesity medications were slightly more likely than other adults to get too little vitamin D from their diet, before any medication (Babazadeh et al., Journal of Nutrition, 2026, DOI (external link)). Get your vitamin D level checked instead of guessing. Evidence: moderate, and stronger if you're low to start.
A basic multivitamin
This is simple gap insurance. When total intake drops, it gets harder to cover the full range of micronutrients, and a plain daily multivitamin covers a lot of small shortfalls cheaply. Think of it as a floor under your micronutrient intake while you're eating less. It won't boost performance. Evidence: reasonable as insurance, not a treatment.
Vitamin B12
Eating less, especially fewer animal foods, can lower B12 over time. So can metformin, which many people with type 2 diabetes take alongside a GLP-1. In the Diabetes Prevention Program Outcomes Study, low or borderline-low B12 was about twice as common on metformin as on placebo at 5 years (Aroda et al., Journal of Clinical Endocrinology & Metabolism, 2016, DOI (external link)). Deficiency causes fatigue and other problems. If you're eating fewer animal foods or take metformin, have your B12 checked before you supplement blindly. Evidence: situational.
Magnesium
People take magnesium for constipation, muscle cramps, or sleep. Some forms, like magnesium citrate, have a mild laxative effect, which is relevant to the constipation problem above. It's reasonable for constipation and for correcting a real shortfall; the sleep and cramp claims are weaker. Evidence: modest.
Electrolytes
If nausea, vomiting, or diarrhea are causing fluid losses, or you're simply drinking less, electrolytes can help you stay hydrated and feel less wiped out. Hydration matters more than usual on these drugs. Most people don't need electrolyte products every day. Evidence: practical for replacing losses.
Cautions
- Supplements aren't regulated like medications. In the U.S., the FDA does not approve dietary supplements for safety or effectiveness before they're sold (FDA (external link)), so quality varies. Look for third-party testing (USP, NSF).
- More is not better. Fat-soluble vitamins (A, D, E, K) and minerals can build up to harmful levels, and megadoses can do more harm than good.
- They can interact. Some supplements affect how medications are absorbed or how your labs read. Fiber is the common one: psyllium labels say to take it at least 2 hours before or 2 hours after any prescription medicine you take by mouth (DailyMed (external link)).
- Watch what counts as protein. Some supplements sold alongside protein, collagen especially, carry protein on the label without the amino acid profile that protects muscle.
- Tell your care team what you're taking. Bring the actual list to appointments. A prescriber or dietitian can help you prioritize, and prune.
Research findings above are attributed to PubMed-indexed articles with DOI links.
This is general education, not medical advice. Supplement needs depend on your labs, your diet, your other medications, and your health history. Talk to your prescriber or a registered dietitian before starting something new, especially if you're managing another condition or taking other medications.