Best Supplements to Take with Metformin (and Which Ones to Avoid)

Jul 9, 2026

Best Supplements to Take with Metformin (and Which Ones to Avoid)

Quick Answer

Yes, most people can safely take supplements while taking metformin.

Metformin is one of the most commonly prescribed medicines for type 2 diabetes and is generally well tolerated. However, long-term treatment has been associated with reduced vitamin B12 levels in some people. Depending on your diet, overall health and medical history, other supplements may also be worth considering.

That doesn't mean everyone taking metformin needs supplements. The right choice will depend on your nutritional intake, how long you've been taking metformin and whether you have any existing vitamin or mineral deficiencies.

In this guide, we'll explain:

Which supplements may be worth considering.
Which supplements should be avoided or used with caution.
What to look for when choosing a high-quality supplement.
When it's worth speaking to your GP or pharmacist.

Pharmacist's Verdict

Question	Answer
Can I take supplements with metformin?	✅ Yes, in most cases.
Should everyone taking metformin take supplements?	❌ No.
Which nutrient is most commonly discussed?	✅ Vitamin B12.
Are there supplements that should be used with caution?	✅ Yes — we'll cover these later in the article.

Where Should You Start?

If you're taking metformin long term, you don't need to fill your cupboard with supplements. Instead, focus on nutrients that are most relevant to metformin and your individual health needs.

Supplement	When to consider it	Why?
Vitamin B12	If you've been taking metformin for several months or years	Long-term metformin use has been associated with reduced vitamin B12 levels in some people.
High-quality multivitamin	If you're looking for general nutritional support	Can help support your overall intake of vitamins and minerals, including vitamin B12.
Vitamin D	If you have limited sun exposure or are at risk of deficiency	Supports normal bones, muscles and immune function.
Fibre	If you're struggling to meet your daily fibre intake	Can help support digestive health and contribute to normal bowel function as part of a balanced diet.
Probiotics	If you experience ongoing digestive side effects	Some people choose to take probiotics to support their gut microbiome, although the evidence remains mixed.

The next section explains who may benefit from each of these supplements and what to look for when choosing a high-quality product.

Supplements That May Be Worth Considering

Vitamin B12

Vitamin B12 is the nutrient most commonly associated with long-term metformin use. If you've been taking metformin for several months or years, particularly at higher doses, it's worth discussing your vitamin B12 status with your GP or pharmacist. This is especially important if you follow a vegetarian or vegan diet or have symptoms such as tiredness, pins and needles or memory problems.

A High-Quality Multivitamin

If you're looking for general nutritional support, a well-formulated multivitamin is often the simplest place to start. Look for one that uses bioavailable nutrient forms, avoids unnecessary fillers and provides comprehensive nutritional support rather than focusing on a single nutrient.

(TRINITY is pharmacist formulated, uses bioavailable nutrient forms and separates nutrients across Morning, Day and Night formulations.)

Fibre

Many adults don't consume enough fibre. If your dietary intake is low, increasing fibre through foods such as wholegrains, fruit, vegetables, beans and pulses should be the first step. Where appropriate, a fibre supplement may also be considered to help increase your daily intake.

Vitamin D

Vitamin D deficiency is common in the UK, regardless of whether you take metformin. If you have limited sun exposure, have been advised your levels are low or are at increased risk of deficiency, supplementation may be beneficial.

Probiotics

Some people experience digestive side effects when starting metformin, such as bloating or diarrhoea. Although the evidence is still evolving, some people choose to take probiotics to support their gut microbiome alongside dietary measures.

Supplements to Avoid (or Use with Caution)

Most supplements can be taken safely with metformin. However, there are a few situations where it's worth being more cautious.

Supplement	Recommendation	Why?
High-dose vitamin B12	⚠️ Usually unnecessary	Unless you've been diagnosed with a deficiency, more isn't always better. Speak to your GP or pharmacist if you're concerned about your B12 levels.
Chromium	⚠️ Use with caution	Chromium may affect blood glucose levels. If you're taking medication for diabetes, discuss supplementation with your healthcare professional first.
High-dose herbal blood sugar supplements	⚠️ Use with caution	Ingredients such as berberine, cinnamon and bitter melon may also lower blood glucose. Taking them alongside metformin may not be appropriate for everyone.
Duplicate supplements	⚠️ Avoid	Check the labels before taking multiple products together, as many multivitamins and individual supplements contain the same vitamins and minerals.

If you have diabetes, it's particularly important to let your GP, pharmacist or diabetes nurse know about any supplements you're taking. This helps ensure they're appropriate for your individual health needs and won't interfere with your diabetes management.

When Is It Worth Seeking Advice?

While most people can safely take supplements with metformin, it's worth speaking to your GP, pharmacist or diabetes nurse if:

You've been taking metformin for several months or years and have never had your vitamin B12 levels checked.
You have symptoms such as persistent tiredness, pins and needles, numbness or memory problems.
You're planning to take supplements marketed for blood sugar control.
You're taking insulin or other diabetes medicines alongside metformin.
You're pregnant, breastfeeding or planning a pregnancy.
You have kidney disease or another long-term medical condition.

Your healthcare professional can advise whether blood tests, dietary changes or targeted supplementation are appropriate. In many cases, simple lifestyle changes and the right supplement—if needed—are more beneficial than taking multiple products without clear evidence.

Frequently Asked Questions

Can I take supplements with metformin?

Yes. Most supplements can be taken safely alongside metformin. However, if you have diabetes, it's always sensible to let your GP, pharmacist or diabetes nurse know about any supplements you're taking.

What are the best supplements to take with metformin?

Vitamin B12 is the nutrient most commonly discussed with long-term metformin use. Depending on your individual needs, a high-quality multivitamin, vitamin D or fibre supplement may also be worth considering.

Does metformin cause vitamin B12 deficiency?

Not always. However, long-term metformin use has been associated with reduced vitamin B12 levels in some people, which is why periodic monitoring may be recommended.

Should I take vitamin B12 with metformin?

Not everyone needs to. If you've been taking metformin for a prolonged period or are at increased risk of vitamin B12 deficiency, speak to your GP or pharmacist about whether supplementation or a blood test is appropriate.

Can I take magnesium with metformin?

Yes. Magnesium can generally be taken safely with metformin. It's not routinely recommended because of metformin itself, but it may be appropriate if your dietary intake is low or you've been advised to increase your magnesium intake.

Can I take probiotics with metformin?

Yes. Some people choose to take probiotics to support their gut microbiome, particularly if they experience digestive side effects such as bloating or diarrhoea. The evidence is still evolving, so probiotics aren't routinely recommended for everyone.

Can I take herbal blood sugar supplements with metformin?

Some herbal supplements, including berberine, cinnamon and bitter melon, may also lower blood glucose. Speak to your GP, pharmacist or diabetes nurse before taking these alongside metformin.

Should I stop taking metformin if I'm worried about vitamin B12?

No. Continue taking metformin exactly as prescribed. If you're concerned about your vitamin B12 levels or think you may have developed a deficiency, arrange a review with your healthcare professional rather than stopping your medication.

Can I take TRINITY with metformin?

For most people, yes. A high-quality multivitamin can be a sensible way to support your overall nutritional intake while taking metformin. If you're choosing a multivitamin, look for one that uses bioavailable nutrient forms and provides comprehensive nutritional support.

References

British National Formulary (BNF). Metformin.
National Institute for Health and Care Excellence (NICE). Type 2 diabetes in adults: management.
NHS. Metformin.
Medicines and Healthcare products Regulatory Agency (MHRA). Metformin and reduced vitamin B12 levels: new advice for monitoring patients at risk.
American Diabetes Association. Standards of Care in Diabetes.
European Food Safety Authority (EFSA). Authorised Health Claims for Vitamins and Minerals.