GLP-1 medications create nutritional conditions that don't exist in normal dieting. Suppressed appetite leads to nutritional gaps. Rapid weight loss depletes certain minerals faster than usual. Changed gut motility creates side effects that require targeted support. Generic supplement advice doesn't account for any of this. Here are the five supplements with the strongest evidence specifically for people on semaglutide and tirzepatide.
1. Creatine Monohydrate — Non-Negotiable
5g daily
Creatine has more clinical evidence for muscle preservation during caloric restriction than any other supplement. Multiple randomized controlled trials show that 5g of creatine monohydrate daily maintains lean muscle mass and strength during significant weight loss. On GLP-1 medications — where rapid, large-volume weight loss is common — this matters more than in any other dietary context. Creatine is inexpensive, safe, and has a strong enough evidence base that it belongs in the same category as adequate protein: not optional.
2. Multi-Strain Probiotic — For GI Side Effects
50 billion+ CFU, 10+ strains
Between 30-40% of GLP-1 users experience significant GI side effects: nausea, constipation, diarrhea, or stomach discomfort. These side effects cause many people to discontinue treatment. GLP-1 medications work partly by slowing gastric emptying — which changes the entire gut environment. A high-quality multi-strain probiotic directly supports this environment. The evidence is strongest for probiotic strains that improve gut motility and reduce nausea. Look for at least 10 strains and 50 billion CFU. Shelf-stable formulas are more practical than refrigerated ones.
3. Magnesium Bisglycinate — Deficiency Accelerates on GLP-1
200-400mg before bed
Magnesium is the most commonly deficient mineral in Western diets. Rapid weight loss makes it worse — magnesium is stored partly in fat tissue and is excreted more rapidly during active weight loss. Deficiency shows up as poor sleep, muscle cramps, fatigue, and constipation. The form matters: magnesium oxide and citrate have laxative effects at therapeutic doses. Magnesium bisglycinate absorbs well without the digestive side effects, making it the right choice for GLP-1 users who already deal with GI sensitivity.
4. Vitamin B12 — Often Low After Dietary Changes
1,000mcg sublingual or methylcobalamin
B12 is found primarily in animal products. GLP-1 users who eat significantly less overall — and particularly those who reduce meat intake — commonly develop B12 insufficiency. Symptoms include fatigue, brain fog, and nerve tingling. Sublingual B12 (dissolved under the tongue) absorbs better than standard swallowed tablets and doesn't require stomach acid for absorption — relevant for users with reduced gastric secretion from GLP-1 medications.
5. Vitamin D3 + K2 — Foundation for Everything Else
2,000-5,000 IU D3 with K2
Vitamin D deficiency is extremely common and affects immune function, bone density, muscle function, and metabolic health. For GLP-1 users specifically: reduced food intake reduces dietary D intake, and rapid weight loss can temporarily reduce D absorption from fat tissue. D3 + K2 is the best combination — K2 ensures calcium goes to bones rather than arteries, which matters more when D levels are actively being corrected.
What About a Multivitamin?
A basic multivitamin is a reasonable addition for GLP-1 users eating significantly less than normal. It won't replace the targeted supplements above — multivitamin doses are too low for magnesium and B12, and they don't include creatine or probiotic strains. Use it as insurance, not a substitute.