Who Should Not Take Glucosamine and Chondroitin
Glucosamine and chondroitin sit on the shelves of almost every pharmacy and supermarket in the UK, and many gym-goers take them as casually as a multivitamin. Yet "available without prescription" is not the same as "suitable for everyone". Our editorial team has gathered what is known about the groups of people for whom these supplements are inadvisable, or who should at least talk to a clinician before starting.
What these supplements are and why people take them
Glucosamine is an amino sugar that the body uses to build glycosaminoglycans, the long chains that give cartilage its ability to hold water and resist compression. Commercial glucosamine is usually sold as the sulfate or hydrochloride salt. Chondroitin sulfate is one of those glycosaminoglycans in its own right and is typically extracted from animal cartilage.
The rationale for taking them is intuitive: if cartilage is made of these molecules, supplying more of them might slow wear or ease pain. In practice the evidence is mixed. The large GAIT trial in the United States found no overall benefit over placebo for knee pain, although a subgroup with moderate-to-severe pain showed a possible signal that later work did not firmly confirm.
A network meta-analysis published in the BMJ in 2010 concluded that, compared with placebo, neither glucosamine, chondroitin nor their combination produced clinically relevant reductions in joint pain or narrowing of joint space. For this reason the NICE osteoarthritis guideline (NG226) advises against offering glucosamine for the management of osteoarthritis on the NHS.
In the UK, glucosamine products are sold mostly as food supplements, while a small number of glucosamine products have previously held medicines licences. Either way, people often assume that a product sold over the counter carries no risks. That assumption is the main reason it is worth knowing the exceptions described below.
Allergies and the source of raw materials
Most glucosamine is produced from the shells of crustaceans such as shrimp, crab and lobster. The allergenic proteins in shellfish are found mainly in the flesh, and purified glucosamine should in theory contain very little of them. Small studies in people with confirmed shellfish allergy have not shown frequent reactions, but the data are limited.
Because of that uncertainty, many manufacturers and pharmacists advise people with a known shellfish allergy to avoid crustacean-derived glucosamine or to choose a product made by fermentation of corn or other non-animal sources. Labels in the UK must declare crustaceans as an allergen where they are an ingredient, so reading the packaging carefully is the first step.
Chondroitin raises a different question. It is usually extracted from bovine, porcine, chicken or shark cartilage. This matters for people following vegetarian, vegan, halal or kosher diets, and for anyone with an allergy to a specific animal protein. Products rarely state the source in large print, so it is worth checking with the brand.
Finally, combination products often contain extra ingredients: MSM, turmeric, hyaluronic acid, collagen, vitamin C or herbal extracts. An allergy or intolerance may be triggered by any of these rather than by glucosamine itself, which is why the full ingredient list should be read, not just the headline.
Blood thinners and other medicines
The most important interaction concerns warfarin. Case reports collected by regulators and reviewed by Knudsen and Sokol describe people whose INR rose, sometimes with bruising or bleeding, after they started glucosamine, with or without chondroitin. The UK Medicines and Healthcare products Regulatory Agency (MHRA) has also highlighted this risk in safety communications.
The mechanism is not fully understood. Chondroitin is structurally related to heparin-like molecules and may have a mild anticoagulant effect, while glucosamine may influence the metabolism of warfarin. Regardless of mechanism, the practical message is clear: anyone on warfarin should not start these supplements without telling the anticoagulation clinic.
Caution is also reasonable for people taking other drugs that affect bleeding:
- direct oral anticoagulants such as apixaban or rivaroxaban;
- antiplatelet drugs, including low-dose aspirin and clopidogrel;
- regular high-dose NSAIDs such as ibuprofen or naproxen;
- supplements with possible antiplatelet effects, for example high-dose fish oil or ginkgo.
There are also theoretical concerns about glucosamine and some chemotherapy agents, and about combining it with medicines for diabetes. People with complex medication lists, particularly older adults, benefit from a pharmacist review before adding any joint supplement.
| Situation | Main concern | Suggested action |
|---|---|---|
| Taking warfarin | Raised INR, bleeding | Avoid unless agreed with clinic; extra INR checks |
| Shellfish allergy | Possible allergic reaction | Choose non-crustacean source or avoid |
| Pregnancy or breastfeeding | No safety data | Avoid |
| Type 1 or type 2 diabetes | Theoretical effect on glucose | Monitor glucose, discuss with GP |
| Asthma | Isolated case reports of worsening | Use with caution, stop if symptoms change |
| Under 18 | Not studied in adolescents | Not recommended |
Diabetes, pregnancy and other special situations
Glucosamine is an amino sugar, and early animal studies suggested it might worsen insulin resistance. A comprehensive review by Simon and colleagues found that oral glucosamine at usual supplement amounts did not meaningfully affect blood glucose or insulin sensitivity in most people, including those with diabetes. Still, individual responses vary, so extra glucose monitoring for the first weeks is sensible.
Pregnant and breastfeeding women are a clear exclusion group, not because harm has been shown but because there are no adequate safety data. With osteoarthritis rare at that stage of life and the evidence of benefit weak, the balance does not favour taking an unstudied supplement.
Several case reports link glucosamine with worsening of asthma, and the product information of licensed preparations has mentioned caution in asthma. The evidence is thin, but people with poorly controlled asthma should watch for any change in symptoms. Similar caution applies to those with significant kidney or liver disease, where clearance may be altered.
Glucosamine sulfate preparations may contain sodium or potassium salts. For most people this is irrelevant, but for those on a sodium- or potassium-restricted diet because of heart or kidney disease, the extra mineral load from daily tablets should be counted. People awaiting surgery are usually asked to stop supplements that may affect bleeding a week or two beforehand.
How to decide whether a supplement makes sense
For athletes without joint disease, there is no good evidence that glucosamine or chondroitin prevents injury or improves recovery. Most studies were done in older adults with established osteoarthritis. Healthy cartilage responds far more to sensible loading, body weight management and muscle strength around the joint.
If someone with joint pain still wants to try a supplement, a time-limited trial is a reasonable approach. Studies typically used around 1,500 mg of glucosamine and 800–1,200 mg of chondroitin daily. If there is no noticeable improvement after about three months, continuing is unlikely to help.
Product quality also varies. Independent analyses have found that the actual chondroitin content of some products differs considerably from the label. Choosing brands that use third-party testing and clearly state the source and salt form reduces that uncertainty.
Above all, persistent joint pain, swelling, locking or instability deserve proper assessment. A supplement can mask symptoms of a meniscal tear, inflammatory arthritis or gout that need a completely different approach.
Conclusions of the editorial team
Glucosamine and chondroitin are generally well tolerated, but they are not risk-free for everyone. People on warfarin or other blood thinners, those with shellfish allergy, pregnant or breastfeeding women and adolescents should avoid them or use them only after professional advice.
People with diabetes, asthma, kidney disease or restricted sodium intake can often take them, but with extra monitoring and a clear plan to stop if problems appear.
Given that the evidence of benefit is modest at best, the question is less "is it safe?" and more "is it worth it?" For many active people, money and effort are better spent on strength work and load management.
If this topic interests you, you may also want to read our pieces on MSM for joints after 40, on how NSAIDs affect training adaptation, and on collagen supplements for tendons.
References
- Clegg DO, Reda DJ, Harris CL, et al. Glucosamine, chondroitin sulfate, and the two in combination for painful knee osteoarthritis. N Engl J Med. 2006;354(8):795–808.
- Wandel S, Jüni P, Tendal B, et al. Effects of glucosamine, chondroitin, or placebo in patients with osteoarthritis of hip or knee: network meta-analysis. BMJ. 2010;341:c4675.
- 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;28(4):540–548.
- Simon RR, Marks V, Leeds AR, Anderson JW. A comprehensive review of oral glucosamine use and effects on glucose metabolism in normal and diabetic individuals. Diabetes Metab Res Rev. 2011;27(1):14–27.
- National Institute for Health and Care Excellence. Osteoarthritis in over 16s: diagnosis and management. NICE guideline NG226. London: NICE; 2022.
