Best Supplements to Take on a GLP-1: 6 Picks Ranked by Evidence

The supplements most worth taking on a GLP-1 cover what you stop eating. That means protein to protect muscle, fiber for constipation, and vitamin D, calcium or B12 if you are low. A 2025 joint advisory from four nutrition and obesity medicine groups says supplements for these at-risk nutrients can be considered, tailored to each person, while calories drop (Mozaffarian 2025, AJCN). Creatine adds a small muscle and strength boost for postmenopausal women who lift (creatine meta-analysis 2026).

How we chose

We ranked each supplement on four things, checked on September 30, 2026:

• Does it solve a real GLP-1 problem? The big ones are muscle loss, constipation and nutrient gaps from eating much less.
• Backing from the 2025 joint advisory of the American College of Lifestyle Medicine, the American Society for Nutrition, the Obesity Medicine Association and The Obesity Society.
• Randomized trial evidence for the supplement itself.
• Safety at normal doses.

1. Protein powder or shakes

Protein is the one thing almost everyone on a GLP-1 struggles to get enough of. When appetite drops, protein often drops with it, and that speeds up muscle loss. Without strength training, about 10% to 15% of the weight women lose on these drugs may come from muscle (Mozaffarian 2025, AJCN).

The advisory notes the standard minimum is 0.8 g of protein per kilogram of body weight a day, with higher targets of 1.2 to 1.6 g/kg proposed during active weight loss. Intake should not drop below 0.4 to 0.5 g/kg, and long stretches at 2 g/kg or more should be avoided (Mozaffarian 2025, AJCN). A shake is the easiest way to close the gap when meals are tiny. More on this in our guide to keeping muscle on a GLP-1.

Best for: everyone on a GLP-1, especially women over 40 and anyone not strength training yet.

Trade-offs: a shake does not replace lifting. Some women find thick shakes worsen fullness or nausea, so smaller servings spread through the day help.

2. Fiber (psyllium)

Constipation is one of the most common GLP-1 side effects, reported in about 24% of people on semaglutide 2.4 mg and 11% on tirzepatide 15 mg in trials (Mozaffarian 2025, AJCN).

A meta-analysis of 16 randomized trials in adults with chronic constipation found fiber supplements helped more people than placebo, with psyllium among the types that worked. Benefits showed at higher doses taken for at least four weeks (van der Schoot 2022, AJCN). The advisory suggests building fiber gradually with fluids, and easing off high-fiber foods in the first days of a new dose if nausea hits (Mozaffarian 2025, AJCN).

Best for: women with constipation or hard stools on a GLP-1.

Trade-offs: gas and bloating, which the meta-analysis also found (van der Schoot 2022, AJCN). Start low, drink plenty of water, and do not add a big dose during a nauseous week.

3. Vitamin D and calcium

Eating less means taking in less vitamin D and calcium, which matters for bone while you lose weight. The advisory lists vitamin D and calcium among the at-risk nutrients worth considering as supplements, tailored to each person (Mozaffarian 2025, AJCN).

Best for: women in or after menopause, women who avoid dairy, and anyone with a low vitamin D blood test.

Trade-offs: more is not better. Dose should match your blood level and diet, which a clinician can check.

4. Vitamin B12

B12 is on the advisory's list of at-risk nutrients when calorie intake falls, and severe fatigue or unusual hair loss can be signs of a deficiency (Mozaffarian 2025, AJCN). Women who also take metformin are at extra risk, since metformin is linked to low B12 (Metformin B12 review, Cureus 2023). Our guide on B12 while on semaglutide covers testing and doses.

Best for: women on metformin, vegetarians and vegans, and anyone with a low level on testing.

Trade-offs: if your level is normal, extra B12 does not boost energy or weight loss.

5. Multivitamin-mineral

A daily multivitamin is a simple safety net when you are eating far less. The advisory names a multivitamin-mineral tablet as an option, and it lists iron, calcium, magnesium, zinc and vitamins A, D, E, K, B1, B12 and C as nutrients of concern, especially below about 1,200 calories a day for women (Mozaffarian 2025, AJCN).

Best for: women eating very little, or who have dropped whole food groups.

Trade-offs: it will not fix a true deficiency that needs a higher targeted dose, and a big pill can be hard to take with nausea.

6. Creatine

Creatine is a well-studied sports supplement that helps muscles do more work. It is not in the GLP-1 advisory, but it targets the muscle-loss problem directly.

A 2026 meta-analysis of seven randomized trials in 608 postmenopausal women found creatine taken at 5 g or more a day with resistance training added a small gain in lean mass and leg strength. Doses of 3 g or less without training did nothing. Side effects matched placebo and kidney tests did not change (creatine meta-analysis 2026). No trial has tested creatine in women on a GLP-1 specifically.

Best for: women who strength train and want to hold onto muscle while losing weight.

Trade-offs: only works with lifting. People with kidney disease should check with a clinician first.

Comparison at a glance

How to choose

Start with protein and, if things slow down, fiber. Those two fix the most common GLP-1 problems. Ask for a basic blood panel to see whether you need vitamin D, B12 or iron rather than guessing. If you lift, creatine is a reasonable add-on. If your hair starts shedding, our piece on hair loss after rapid weight loss explains why and what helps.

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