Which supplements should you take on Mounjaro — and which ones to rethink

The gap that a reduced appetite can quietly open

Tirzepatide works, in part, by slowing gastric emptying and dampening hunger signals. That's the mechanism behind the weight loss. It also means that on days when a bowl of soup is genuinely all you want, your total intake of protein, iron, B12, folate, calcium and zinc can fall below what your body needs, not dramatically, but consistently enough to matter over months.

This isn't unique to Mounjaro: the NHS patient information for tirzepatide notes reduced appetite as one of the medicine's expected effects, and nutritional adequacy during treatment is something a prescriber or dietitian will factor in. The practical upshot is that supplement decisions on Mounjaro aren't really about adding extras, they're about plugging the gaps that a smaller plate creates.

A quick habit worth building: before your next repeat order, check your average daily protein intake for a single day using the labels on whatever you actually ate. If it's consistently below 60–80g, that's worth raising with your prescriber or a registered dietitian. Takes less than a minute and gives you something concrete to act on. You can also browse our overview of Mounjaro and supplementation for more context.

The supplements most people on Mounjaro genuinely benefit from

Vitamin D is the most straightforward. The NHS recommends that everyone in the UK considers a daily 10 micrograms (400 IU) supplement through autumn and winter, because sunlight exposure alone is insufficient. For people whose food variety has reduced on treatment, it becomes more relevant, not less. A standard daily supplement at that dose is safe and inexpensive.

A broad-spectrum multivitamin covering the B vitamins (B1, B6, B9/folate, B12), zinc, iron and magnesium covers most of the micronutrient bases without over-supplementing. Choose one that's taken with food rather than on an empty stomach, Mounjaro already slows digestion, so fat-soluble vitamins absorb better alongside a meal, however small.

Protein deserves its own category. It's not a supplement in the traditional sense, but protein powders or shakes are a practical tool for people who find their appetite too suppressed to hit their target through food alone. Whey or soy-based options mixed into a smoothie or yoghurt are easy to tolerate even when nausea is present. This matters because muscle mass is protective during any period of significant weight loss, preserving it is part of what makes the outcome durable. Our guide to specific supplements to take with Mounjaro goes into more detail on protein targets and timing.

Omega-3 fatty acids (EPA and DHA, typically from fish oil) are worth considering if oily fish has dropped out of your diet. They have a reasonable evidence base for cardiovascular and metabolic health, and are unlikely to cause any problems alongside tirzepatide at standard doses.

Supplements that deserve a pause before you add them

Fat-soluble vitamins in high doses (particularly vitamin A and vitamin E) can accumulate because tirzepatide slows gastric emptying, potentially altering absorption patterns. Standard multivitamin levels are fine; megadose single-nutrient supplements are worth discussing with a prescriber first.

Herbal and botanical supplements are a more complex conversation. Some (St John's Wort is the clearest example) affect liver enzymes that process other medicines. Tirzepatide itself isn't metabolised by the same pathways, but if you're taking any other prescription medication alongside it, herbal products can complicate the picture. Our page on tirzepatide and weight-loss supplements covers this in more depth.

Iron supplements specifically can contribute to constipation, which is already a common side effect during the early weeks of Mounjaro. If a blood test shows you need iron supplementation, the timing and form (liquid, capsule, alternate-day dosing) are worth discussing rather than defaulting to a standard over-the-counter dose. The same logic applies to magnesium: the oxide form is more likely to cause loose stools, while magnesium glycinate or citrate is gentler on the gut.

For a fuller picture of tirzepatide as a treatment (including how the medicine itself works) the tirzepatide overview on this site is a good starting point.

Collagen, creatine and the supplements people ask about most

Collagen supplements come up frequently in this context, partly because skin elasticity is a genuine concern during rapid weight loss. The evidence for dietary collagen improving skin structure is more modest than the marketing suggests, but collagen peptide powders are generally safe alongside Mounjaro and may have a modest benefit for skin and joint comfort. We've looked at this specifically in our guide on Mounjaro and collagen.

Creatine monohydrate is one of the most studied sports-nutrition supplements in existence. There's no interaction concern with tirzepatide, and it has a reasonable evidence base for supporting muscle retention during weight loss, particularly if you're combining treatment with resistance training. Standard doses (3–5g daily) are fine for most people.

Fibre supplements (psyllium husk, for instance) can help if constipation is proving difficult to manage through diet. Take them with a full glass of water, not alongside the Mounjaro pen itself.

Whatever you decide to add, it's worth checking with your prescriber, especially at the point of starting treatment or increasing your dose, when the digestive side-effect picture can shift. If you're weighing up whether Mounjaro is the right treatment for you in the first place, our guide to whether Mounjaro is right for you may help you frame that decision. Details on the private prescription process and what it involves are on the Mounjaro cost and treatment page.

When you're ready to talk it through properly, start your free consultation with our prescribers.