"What should I be taking?" is one of the most common questions in GLP-1 communities, and it is usually answered by strangers with a list. This article will not do that. Not out of caution for its own sake, but because the honest answer to the question is a different question, and getting the order right actually matters here.
What follows is what is known, what is genuinely not known, and what to raise at your next appointment.
The mechanism is simply eating less
Start with the plain version, because a lot of anxious internet writing obscures it. GLP-1 medications are not stripping nutrients out of your body. They reduce how much you eat, sometimes substantially, and eating substantially less means taking in less of everything that food carries. Protein, fiber, vitamins and minerals all arrive on the same plate.
That framing is useful because it points at the fix. The first response to a smaller intake is usually to make what you do eat count, not to buy a bottle. Our guides to protein goals and fiber cover the two that slip first and most visibly.
It also explains why the risk is not uniform. Someone eating varied meals at a smaller volume is in a different position from someone whose diet has narrowed to two or three tolerable items, and neither is in the position of someone who has barely eaten for a fortnight through a rough dose step.
What a large observational study reported
There is now some scale to the data, and it is worth reporting carefully.
In a large records-based study of roughly 461,000 people taking GLP-1 medications, about 12.7 percent had a newly diagnosed nutritional deficiency within six months. Vitamin D was the most common at about 7.5 percent, and the overall figure rose to about 13.6 percent by twelve months.
Now the hedging, which is not a formality. This is an observational finding drawn from health records. It describes what was documented in a large population of people taking these medications, and it does not establish that the medication caused the deficiencies. People starting a GLP-1 are also being seen more often and tested more often, and testing more finds more. Deficiencies that predated treatment can surface as new diagnoses simply because someone finally ordered the panel.
Most importantly, a population percentage is not a forecast for you. It is not a prediction that you will develop a deficiency, and it is not a reason to start taking anything. What it reasonably supports is a modest conclusion: this is worth paying attention to, and worth asking about.
Which nutrients come up most often
The literature repeatedly implicates a fairly consistent set: vitamin D, the B vitamins including thiamine and B12, iron, calcium, magnesium and potassium.
Treat that as a list of things worth asking about, not a shopping list. It is exactly the sort of list that gets screenshotted and turned into a stack of bottles, which is the opposite of the point.
One entry deserves naming separately. Metformin is independently associated with lower vitamin B12, so anyone taking metformin alongside a GLP-1, a very common combination in type 2 diabetes, has a specific and concrete reason to ask whether B12 should be checked. That is a good question to walk into an appointment with.
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The honest gap: there are no consensus guidelines
This is the part most articles on this subject skip, and it changes how you should read everything else.
There are currently no consensus guidelines for micronutrient monitoring in people taking GLP-1 medications. No agreed panel, no agreed schedule, no settled standard of care for who gets tested and how often.
Reviews have made suggestions. Checks commonly proposed include a complete blood count, a metabolic panel, vitamin B12, vitamin D, iron studies and albumin, taken before starting and periodically afterward. That is a reasonable starting point for a conversation, and it is the sort of thing worth mentioning by name at an appointment. It is not a protocol you can hold a clinician to, because none exists.
The practical consequence is that practice varies. Two reasonable clinicians may take different approaches, and neither is doing anything wrong. It also means the burden of raising the topic often falls to you, which is a slightly uncomfortable thing to say and also true.
Anyone claiming there is a standard GLP-1 supplement protocol is either selling something or repeating someone who is.
Test first, then treat what is actually low
Which brings us to the one recommendation this article does make, and it is about sequence rather than substance.
Test first. Then treat what is actually low, under clinical supervision.
Supplementing blind is not a neutral act. Three reasons it goes wrong:
- It can mask a problem that needed investigating. Fatigue treated with a guessed supplement is fatigue that has not been explained. If something is genuinely low, the useful question is often why, and a bottle can quietly delay that question for months.
- Some nutrients are harmful in excess, not merely wasted. Iron is the clearest example: excess iron is a real harm rather than an expensive way to make nothing happen. Several of the minerals on the list above are also cleared by the kidneys, which matters if kidney function is reduced.
- You cannot tell from the inside. The symptoms attributed to low vitamin D, low B12 and low iron overlap heavily with each other, with ordinary GLP-1 side effects, and with being tired. A blood test distinguishes them. Guessing does not.
Testing turns all of this into something specific: a number, a decision, and a follow-up test to see whether the decision worked.
Who should ask before changing anything
A few situations make the conversation more important rather than less.
Pregnancy changes both the nutrient picture and the safety picture, and nothing should be started or stopped without clinical input. Kidney disease matters because reduced kidney function affects how minerals are cleared, which is why potassium and magnesium in particular are questions for a clinician rather than a shelf. And anyone already taking supplements or other medications should bring the actual containers, or photographs of the labels, since interactions and unintentional double dosing are far more common than people expect once a routine has a few bottles in it.
On product quality generally, we have written about it at length in the context of protein shakes on a GLP-1: supplements are not reviewed by the FDA for safety, quality or effectiveness before they go on sale, and independent testing keeps finding that labels and contents do not always agree. That article covers what third-party certification does and does not verify. The same logic applies to anything else in a bottle.
What to bring to the appointment
Lab results are far more interpretable with context, and intake history is the context. A clinician deciding whether a borderline result matters is helped enormously by knowing whether you have been eating well at a smaller volume or barely eating at all.
So bring three things. Your dose log, including where you are on the ladder and when the last increase was, since a rough stretch usually maps onto a step. A realistic picture of what you have actually been eating, not an idealized one. And any specific symptoms with rough dates: fatigue, hair shedding, feeling cold, unusual bruising, low mood.
In GLP 1 Tracker App, doses, food, protein, water, weight and a side effect diary with severity all sit in one place, so that picture is a scroll rather than a reconstruction. Premium adds CSV or JSON export if a clinician or dietitian wants the underlying data. Our guide to preparing for appointments covers how to get through the questions efficiently, and hair shedding on a GLP-1 covers one of the symptoms that most often prompts this exact conversation.
The takeaway
Eating much less means taking in less of everything, and that is the whole mechanism. Large observational data has reported newly diagnosed deficiencies in a meaningful share of people on these medications, with vitamin D most common, and that is a reason to pay attention rather than a prediction about you. Vitamin D, B vitamins including thiamine and B12, iron, calcium, magnesium and potassium are the ones that come up; metformin makes B12 a specific question. There are no consensus monitoring guidelines yet, which is why this is a conversation rather than a checklist. And the order is the part to hold onto: test first, then treat what is actually low, under clinical supervision. A bottle bought on a stranger's recommendation answers a question nobody asked about your body.
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Frequently asked questions
Do GLP-1 medications cause vitamin deficiencies?
The more accurate framing is that eating substantially less means taking in less of everything, micronutrients included. The medication is not stripping nutrients out of you; reduced intake is doing the work. Observational data has reported newly diagnosed deficiencies in a meaningful share of people taking these medications, but records-based findings describe what was observed in a population and do not establish cause or predict what will happen to any one person.
What vitamins should I take on Ozempic or Wegovy?
We do not recommend any supplement, any dose or any brand, and you should be wary of any website that does without knowing your labs. The order that makes sense is testing first, then treating what is actually low, under clinical supervision. Supplementing blind can mask a problem that needed investigating, and some nutrients, iron in particular, are harmful in excess rather than simply wasted.
Should I get blood tests while I am on a GLP-1?
It is a reasonable thing to raise with your prescriber. Reviews have suggested checks such as a complete blood count, a metabolic panel, vitamin B12, vitamin D, iron studies and albumin, before starting and periodically afterward. That is a suggestion in the literature rather than a settled protocol, so what is appropriate for you depends on your history, your other medications and your clinician's judgment.
Are there official guidelines for nutrient monitoring on GLP-1s?
No. There are currently no consensus guidelines for micronutrient monitoring in people taking GLP-1 medications. That is the honest state of the field, and it is precisely why this is a conversation to have with your clinician rather than a protocol to follow off a website. It also means practice varies: two reasonable clinicians may take different approaches, and asking directly is better than assuming.
Do I need vitamin B12 if I take metformin and a GLP-1?
It is a specific question worth raising rather than acting on alone. Metformin is independently associated with lower vitamin B12, so people taking it alongside a GLP-1 have a particular reason to ask whether B12 should be checked. Whether anything needs doing about it depends on the result, and that is a decision for your prescriber rather than something to start on your own.