There are hundreds of supplements you could take. There are five the research keeps pointing to for someone on a GLP-1. Here they are, in order of evidence-per-dollar-per-effort.
1. Creatine monohydrate: 5 g/day
The best-studied ingredient in sports nutrition. Preserves strength and helps hold onto lean mass in a calorie deficit. See the dedicated post on creatine for the full breakdown.
2. HMB: 3 g/day
HMB is a metabolite of leucine that the research links to reduced muscle protein breakdown. The catch: the effective dose is 3 g. Most stacks put in 500 mg or a token amount, which does not match what the studies use.
3. Vitamin D3 with K2: 2,000 IU D3, 150 mcg K2 MK-7
D3 alone is easy. Pairing it with K2 is what the research supports for actually directing the extra calcium your body absorbs into bone rather than soft tissue. Rapid weight loss puts bone density at risk, so this pair earns its space.
4. Electrolytes: sodium, potassium, magnesium
Cramps, headaches, and poor sleep on a GLP-1 are almost always downstream of eating less salt and fewer mineral-rich foods. Most people need to add electrolytes deliberately once appetite drops. See the cramps post for numbers.
5. Soluble fiber and lactase in the serving
Acacia gum is a gentle, well-tolerated soluble fiber that stays low viscosity and dissolves clear instead of turning to gel. At 3 g, it contributes toward total daily fiber.
The lactase is there to break down the small amount of lactose a whey isolate still carries.