If you are taking a GLP-1 medication, the supplement industry has spent the last two years shouting at you from two directions at once — sell you something to replace the drug, or sell you a twelve-capsule "companion stack" to take alongside it. This article does neither. It looks at what actually happens nutritionally when your appetite drops by a fifth, what the claims data says about how often that turns into a measurable deficiency, and which of it is worth acting on. Most of the answer is food, not capsules. The parts that are not, we name specifically.
The Problem Is Arithmetic, Not Pharmacology
GLP-1 receptor agonists work largely by making you want less food. That is the point, and it is why they work. But nutrients arrive in food, and micronutrient requirements do not fall just because portions do. Cut intake by roughly a fifth and hold it there for a year, and the gap between what you need and what you eat has to show up somewhere.
It does, and it has been measured at scale. A retrospective analysis of de-identified claims data covering 461,382 adults newly prescribed a GLP-1 receptor agonist, none of whom had a prior nutritional deficiency diagnosis, tracked what was diagnosed afterwards (Butsch et al., 2025, Obesity Pillars; PMID: 40584822).
| Newly diagnosed after starting a GLP-1 | Within 6 months | Within 12 months |
|---|---|---|
| Any nutritional deficiency | 12.7% | 22.4% |
| Vitamin D deficiency | 7.5% | 13.6% |
| Nutritional anaemia | 2.1% | 4.0% |
Read that carefully, because it is easy to over-read. Roughly one in five had a deficiency diagnosed within a year — which is a real signal and also a claims-data signal, meaning it reflects what clinicians coded, not a systematic screen of everyone. The cohort was mostly people with type 2 diabetes, mainly female, average age around 53. It tells you this is common enough to plan for. It does not tell you that you personally have a deficiency, and it is not a reason to buy nine supplements on spec.
The Bigger Issue Is Muscle, and It Is Not a Supplement Problem
Before any capsule, this is the thing that deserves your attention. When people lose weight on these medications, a substantial share of what leaves is not fat: lean mass can account for something like 40% to 60% of total weight lost. That matters for strength, for metabolic rate, and for what happens if you ever come off the drug.
The two interventions with the best evidence here are unglamorous and neither is sold in a bottle:
- Resistance training, two to three times a week. This is the single highest-value thing on the entire page. No supplement substitutes for the signal that loading a muscle sends.
- Protein, deliberately and early in the day. When total intake shrinks, protein is the macronutrient most likely to get squeezed out — it is filling, and appetite suppression hits it hardest. Prioritising it at the first meal, when appetite is usually highest, is the practical fix.
Any "GLP-1 companion" marketing that leads with exotic ingredients and mentions resistance training in passing has its priorities backwards. Get those two right and the rest is fine-tuning.
Where Magnesium Genuinely Earns a Place
Magnesium comes up constantly in this context, usually for the wrong reason and occasionally for a very good one. Two things are worth separating.
Constipation — and a form choice that actually matters
Slowed gastric emptying is part of how these drugs work, and constipation is one of the most common consequences. This is the one place in this article where the form of magnesium is the whole point.
Magnesium citrate is osmotically active — it draws water into the intestine, which is precisely why higher doses of it are sold as a laxative. For most uses that is a side effect to be managed. Here, it is the mechanism you want. Magnesium glycinate, by contrast, is chosen specifically because it does not do this, which makes it the wrong tool for this particular job and the right one if you are taking magnesium at night and do not want to be woken.
A formula containing both covers the two behaviours, and our glycinate versus citrate guide explains why the popular "glycinate is simply better" claim rests on a comparison that has never been run in humans. Add fibre gradually rather than all at once, and keep fluid intake up — magnesium is not a substitute for either.
Intake gaps and muscle function
Magnesium is a cofactor in muscle and nerve function and in muscle protein synthesis, and population intake was already marginal before appetite suppression entered the picture — roughly 48% of US adults fall below the estimated average requirement. Eat less food and that gap widens by simple arithmetic.
Be clear about what this is and is not. It is a reasonable argument for covering a nutrient you are probably now short of. It is not evidence that magnesium preserves lean mass on a GLP-1 — no trial has tested that, and anyone implying it has is inventing a finding. Read it as filling a gap, not as a muscle intervention.
A Realistic Priority Order
| Priority | What | Why it sits here |
|---|---|---|
| 1 | Resistance training and protein | Addresses the largest measurable downside of the therapy. Not a supplement. |
| 2 | Ask your prescriber for bloodwork | Vitamin D, B12, ferritin and full blood count. Test, then treat — this is cheaper than guessing. |
| 3 | Vitamin D if you are low | The most commonly diagnosed deficiency in the cohort above. Dose should follow a blood level. |
| 4 | Magnesium | Common intake shortfall; citrate helps with regularity specifically. |
| 5 | A plain multivitamin | Reasonable insurance on a much smaller total food intake. Trials testing this specifically are running now. |
Note what is not on that list: nothing exotic, nothing branded, nothing at position one. If a companion protocol you have been sold inverts this order, that tells you what it was designed to do.
Berberine: Please Do Not Read This as an Exit Strategy
We sell berberine, so let us be direct about it rather than leave you to infer.
Berberine has genuine glycemic evidence. A systematic review and meta-analysis of 37 studies in 3,048 patients with type 2 diabetes found pooled reductions in fasting plasma glucose of 0.82 mmol/L, HbA1c of 0.63 percentage points, and two-hour plasma glucose of 1.16 mmol/L (Xie et al., 2022, Frontiers in Pharmacology; PMID: 36467075). That is a real effect on real endpoints.
It is also not a GLP-1 drug and it is not close to one. The "nature's Ozempic" framing collapses on inspection: berberine's GLP-1-related mechanism comes largely from animal and cell work, human evidence for meaningful GLP-1 activity from supplementation is weak, and typical weight change in trials is on the order of a few pounds over eight to twelve weeks. Its closer comparison is metformin, through the AMPK pathway. We take that apart properly in our berberine guide.
Do not add berberine to a GLP-1 medication, or to any glucose-lowering drug, without your prescriber's involvement.
Two agents that lower blood glucose taken together can lower it further than either alone. Berberine also inhibits CYP3A4, an enzyme that metabolises a long list of common medications, which makes interactions plausible well beyond diabetes drugs. This is a genuine safety point, not boilerplate — and it applies just as much to stopping a prescription in favour of a supplement, which is not a decision to make from a product page.
Questions People Actually Ask
Will supplements stop me losing muscle?
Not on their own, and no supplement has been shown to. Protein intake and resistance training are the interventions with evidence behind them. Micronutrients matter because deficiency makes everything harder, not because any of them preserves lean mass by itself.
Do I need a specific "GLP-1 support" product?
Almost certainly not. The needs described here — protein, vitamin D if you are low, magnesium, a basic multivitamin — are met by ordinary products at ordinary prices. A specialised label mostly buys you the label. Judge these products by their Supplement Facts panel against what you actually need, and be sceptical of proprietary blends that hide per-ingredient amounts.
Can I take magnesium at the same time as my injection?
Timing relative to the injection is not the relevant question, since these are weekly or daily medications with effects that persist. The practical consideration is your own comfort: if you are using citrate for regularity, take it when being near a bathroom is convenient, and if nausea is an issue, take magnesium with food rather than on an empty stomach.
What about when I come off the medication?
This is the question worth planning for early, and it is a clinical one. What is worth knowing is that muscle you kept during treatment is muscle you do not have to rebuild afterwards, which is the practical reason the training-and-protein advice is at position one rather than buried at the end.
Is nausea a nutrient problem?
Usually it is a dose and titration problem, and it belongs with your prescriber rather than in a supplement plan. Where it becomes a nutrition issue is indirectly: persistent nausea shrinks intake further, which widens exactly the gaps described above.
The Short Version
- In a cohort of 461,382 new GLP-1 users, a nutritional deficiency was diagnosed in 22.4% within twelve months, vitamin D most often. Common enough to plan for; not a diagnosis of you.
- Lean mass can be 40–60% of the weight lost. Resistance training and protein are the response, and no capsule replaces them.
- Test before you supplement. Vitamin D, B12, ferritin and a full blood count, via your prescriber.
- Magnesium has two honest roles here: covering a widespread intake shortfall, and — as citrate specifically — helping with constipation.
- Berberine is not a replacement for these medications, and combining it with any glucose-lowering drug needs prescriber involvement.
Where 4Well fits — and where it does not
Magnesium Advanced Complex contains both citrate and glycinate, which covers the regularity use and the evening use. Check the elemental magnesium figure on the panel, and note the formula contains 5-HTP — read the interaction note if you take any serotonergic medication.
We do not sell protein powder, vitamin D or a multivitamin, and those occupy the top of the priority list above. We would rather tell you that than pretend the list starts where our catalogue does.
References
- Scott Butsch W et al. Obes Pillars 2025;15:100186. PMID: 40584822
- Xie W et al. Front Pharmacol 2022;13:1015045. PMID: 36467075
This article is for general education and is not medical advice. These statements have not been evaluated by the Food and Drug Administration. These products are not intended to diagnose, treat, cure, or prevent any disease. Never start, stop or change a prescription medication based on this article. If you are taking a GLP-1 receptor agonist, discuss supplementation and monitoring with the clinician who prescribed it.
