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Is Glucosamine Bad for You? Side Effects and Who Should Ask First
In this article
- What are the side effects of glucosamine?
- Who should not take glucosamine, or should ask first?
- Glucosamine and warfarin
- Glucosamine and shellfish allergy
- Glucosamine and diabetes: does it raise blood sugar?
- Is glucosamine safe for the liver and kidneys?
- What not to mix with glucosamine
- Why do doctors not recommend glucosamine?
- Is it safe to take glucosamine every day, and for how long?
- Frequently asked questions
No, glucosamine is not bad for you. For most adults it is one of the better-tolerated supplements: across twenty randomised trials, side effects were no more frequent on glucosamine than on placebo, and the ones reported were mild and digestive.1 The better question is who should ask first: people on warfarin, after more than 40 reports of clotting times rising; shellfish allergy with a shell-derived product; diabetes, where the advice is to monitor, not avoid; glaucoma; and pregnancy, where there are no trials.2, 3, 4 Kidney and liver damage, atrial fibrillation and dementia do not hold up against the evidence.
- Side effects in trials: same as placebo; nausea, heartburn, wind, loose stools or constipation and headache in a small minority
- Kidneys and liver: no harm in trials; a handful of single case reports, none proving cause
- Every day, long term: trials ran for three years with no safety difference from placebo
What are the side effects of glucosamine?
Mild and uncommon. The Cochrane review of 20 randomised trials in 2,570 people found adverse reactions on glucosamine 0.97 times as likely as on placebo, and the three-year trial of glucosamine sulphate recorded no difference in safety or in reasons for dropping out.1, 5 In GAIT, the largest trial, adverse events were mild, infrequent and evenly spread across all groups.6 The UK prescribing reference for glucosamine as a licensed medicine lists constipation, diarrhoea, stomach discomfort, nausea, headache and tiredness as common, and flushing and skin rashes as uncommon. Taking them with a meal helps.
Who should not take glucosamine, or should ask first?
| Situation | What is known | What to do |
|---|---|---|
| Warfarin or another coumarin anticoagulant | More than 40 case reports of a raised INR after starting glucosamine, mostly symptomless, some with bleeding; the INR usually fell on stopping2, 3 | Tell your GP or anticoagulant clinic before starting; expect extra INR checks |
| Shellfish allergy | Glucosamine comes from the shell, the allergen from the flesh; 15 shrimp-allergic adults tolerated 1,500 mg in a blinded challenge, but UK labels still warn7 | Choose a vegan glucosamine, made without shellfish |
| Type 2 diabetes | HbA1c unchanged over 90 days in a randomised trial; fasting glucose unchanged in trials up to three years8, 9 | Take it; check your readings in the first few weeks |
| Glaucoma or raised eye pressure | A 2013 case series of raised intraocular pressure, reversible on stopping4 | Mention it to your optometrist or eye clinic |
| Pregnancy and breastfeeding | No trials | Leave it until afterwards |
| Thyroid condition or levothyroxine | Some joint products include seaweed, which can be high in iodine10 | Ask your GP if the label lists bladderwrack or kelp |
Glucosamine and warfarin
This is the one interaction that matters. In 2011 the European Food Safety Authority reviewed more than 40 reports to drug-monitoring agencies of the INR, the measure of warfarin's effect, rising after people on coumarin anticoagulants started glucosamine. Most rises caused no symptoms; some caused bleeding, and one left a patient in a persistent vegetative state. In most cases the INR fell back when glucosamine was stopped, which is what makes the link convincing; the mechanism is unknown.2, 3 If you take warfarin, acenocoumarol or phenindione, tell your GP or anticoagulant clinic before starting glucosamine. The newer anticoagulants are not the subject of the reports, but tell your prescriber either way.
Glucosamine and shellfish allergy
Most glucosamine is made from the shells of prawns, crabs and lobsters, and UK labels carry a crustacean warning. The allergen, though, is tropomyosin, a protein in the flesh, and when 15 adults with proven shrimp allergy took 1,500 mg of shrimp-derived glucosamine in a double-blind challenge, none reacted.7 That is one small study and a label warning is a label warning, so the practical answer is a vegan glucosamine: the same molecule, made from plant or microbial sources without shellfish. Check the glucosamine milligrams per serving against the 1,500 mg the positive sulphate trials used; glucosamine has no authorised health claim in Great Britain, so what the trials found is reported on this page as evidence. Some vegan blends add a seaweed complex, and bladderwrack can be high in iodine, so anyone with a thyroid condition or on levothyroxine should check with their GP first; the warfarin rule applies to any glucosamine, whatever else is in the capsule.
Glucosamine and diabetes: does it raise blood sugar?
Not at supplement doses, in the trials. The worry came from rat experiments in which infused glucosamine produced insulin resistance at concentrations 100 to 200 times what 1,500 mg by mouth produces.11 In people, a 90-day randomised trial in type 2 diabetes found no change in HbA1c, and a review of the long-term trials, including people with diabetes and pre-diabetes, concluded there is no effect on fasting glucose at any oral dose.8, 9 A few small studies in people with impaired glucose tolerance saw a dip in insulin sensitivity, so take it and check your readings in the first few weeks. Does glucosamine make you gain weight deals with the related myth.
Is glucosamine safe for the liver and kidneys?
At normal doses there is no evidence of harm to either. Trials running up to three years and a safety review of data from 3,063 participants found no adverse effects on blood, urine or stool measures.5, 11 Beyond that there are single case reports: a few of interstitial nephritis, an inflammatory kidney reaction, and isolated reports of liver injury, which the US National Library of Medicine's liver-injury database judges must be very rare if they occur at all.12 A case report cannot show that the supplement caused what happened. If you have chronic kidney disease, ask your renal team.
What not to mix with glucosamine
Warfarin and the other coumarins, as above. Nothing else is established. Lists online add chemotherapy and paracetamol; these rest on theory, not on any clinical report. Chondroitin, MSM and collagen have no known harmful interaction with glucosamine, though chondroitin lowered blood glucosamine in one study;6 collagen and glucosamine together covers that pairing.
Why do doctors not recommend glucosamine?
Because the average effect in the trials is small, and NHS guidance is written on averages and cost. The 2010 network meta-analysis of ten large trials in 3,803 people found an average effect on pain too small to be clinically relevant, while the Cochrane review found that glucosamine sulphate, in the preparation most of the positive trials used at 1,500 mg a day, improved pain and function against placebo, and individual response varies more than the averages show.1, 14 UK guidance does not recommend glucosamine on the NHS and GPs no longer prescribe it, yet glucosamine sulphate was for years a licensed medicine in the UK for mild-to-moderate knee osteoarthritis, so the question was never safety.15 The Wellgard joint health guide sets out the trials, and what is the best joint supplement compares glucosamine with the alternatives.
Is it safe to take glucosamine every day, and for how long?
Yes, daily is how it was tested: every trial dosed it every day, and the longest ran for three years with no safety difference from placebo.5 Beyond three years there is only cohort data, and UK Biobank's long-term users showed no excess of deaths or cardiovascular events.13 A missed day does not matter, and nothing happens when you stop. The fair test is personal: take it daily for three months, judge your pain and stiffness against where you started, and stop if nothing has changed; if it has earned its place, there is nothing in the evidence against continuing.
Frequently asked questions
Does the NHS recommend glucosamine?
No. GPs no longer prescribe glucosamine or chondroitin on the NHS, and UK guidance says not to offer it, because the evidence of benefit is not strong enough for NHS funding.15
What are the negative side effects of glucosamine chondroitin?
The same as glucosamine alone: digestive upset in a minority, and the warfarin interaction, which chondroitin shares. In GAIT the combination's adverse events matched placebo.6
Does glucosamine cause atrial fibrillation or palpitations?
Not in people. The worry comes from animal work at high doses; in UK Biobank, regular users had fewer cardiovascular deaths, not more, an observational finding and not a benefit claim.13
Does glucosamine cause dementia?
No. In about 290,000 UK Biobank participants followed for about ten years, habitual glucosamine use was not associated with dementia; an earlier analysis of the same cohort found a lower incidence among users.16
Sources
- Towheed TE, et al. Glucosamine therapy for treating osteoarthritis. Cochrane Database of Systematic Reviews, 2005. PubMed 15846645.
- EFSA Panel on Dietetic Products, Nutrition and Allergies. Statement on the safety of glucosamine for patients receiving coumarin anticoagulants. EFSA Journal, 2011. PubMed 42015979.
- Knudsen JF, Sokol GH. Potential glucosamine-warfarin interaction resulting in increased international normalized ratio: case report and review of the literature and MedWatch database. Pharmacotherapy, 2008. PubMed 18363538.
- Murphy RK, et al. Oral glucosamine supplements as a possible ocular hypertensive agent. JAMA Ophthalmology, 2013. PubMed 23702812.
- Reginster JY, et al. Long-term effects of glucosamine sulphate on osteoarthritis progression: a randomised, placebo-controlled clinical trial. Lancet, 2001. PubMed 11214126.
- Clegg DO, et al. Glucosamine, chondroitin sulfate, and the two in combination for painful knee osteoarthritis. New England Journal of Medicine, 2006. PubMed 16495392. Jackson CG, et al. (GAIT pharmacokinetic study), 2010, Osteoarthritis and Cartilage. PubMed 19912983.
- Villacis J, et al. Do shrimp-allergic individuals tolerate shrimp-derived glucosamine? Clinical and Experimental Allergy, 2006. PubMed 17083356.
- Scroggie DA, et al. The effect of glucosamine-chondroitin supplementation on glycosylated hemoglobin levels in patients with type 2 diabetes mellitus. Archives of Internal Medicine, 2003. PubMed 12860582.
- Simon RR, et al. A comprehensive review of oral glucosamine use and effects on glucose metabolism in normal and diabetic individuals. Diabetes/Metabolism Research and Reviews, 2011. PubMed 21218504.
- NHS. Iodine: vitamins and minerals. nhs.uk/conditions/vitamins-and-minerals/iodine.
- Anderson JW, et al. Glucosamine effects in humans: a review of effects on glucose metabolism, side effects, safety considerations and efficacy. Food and Chemical Toxicology, 2005. PubMed 15621331.
- LiverTox: Clinical and Research Information on Drug-Induced Liver Injury. Glucosamine. National Institute of Diabetes and Digestive and Kidney Diseases, 2012. PubMed 31643282.
- Li ZH, et al. Associations of regular glucosamine use with all-cause and cause-specific mortality: a large prospective cohort study. Annals of the Rheumatic Diseases, 2020. PubMed 32253185.
- Wandel S, et al. Effects of glucosamine, chondroitin, or placebo in patients with osteoarthritis of hip or knee: network meta-analysis. BMJ, 2010. PubMed 20847017.
- NHS. Osteoarthritis: treatment. nhs.uk/conditions/osteoarthritis/treatment.
- Ai B, et al. No associations between glucosamine supplementation and dementia or Parkinson's disease: findings from a large prospective cohort study. Journals of Gerontology Series A, 2024. PubMed 37158699.
This article is general information, not medical advice. Joint pain with swelling or heat, or pain after an injury, needs a GP, and if you take warfarin or another anticoagulant, have diabetes or are pregnant, speak to your GP or pharmacist before starting glucosamine.
