Glucosamine and Chondroitin: Evidence, Side Effects, and Shellfish and Warfarin Cautions
What trials and guidelines say about glucosamine and chondroitin for osteoarthritis, the GAIT trial, side effects, and cautions for warfarin, shellfish allergy, diabetes and pregnancy.
Content last updated . This page has not been medically reviewed.
Evidence labels used here: mixed, insufficient evidence, no good evidence of benefit, promising but limited, evidence of harm (for the warfarin signal, as case reports).
What they are
According to NCCIH, glucosamine (as glucosamine sulfate or glucosamine hydrochloride) and chondroitin (as chondroitin sulfate) are sold in the US as dietary supplements, separately or together. [1] NCCIH adds that in some other countries certain preparations are prescription drugs. [1] Forms matter: NCCIH reports that in a 2014 analysis, the prescription formulation had more favorable results, but most of those studies had a high risk of bias. [1] Do not assume results for one form apply to another.What research found
| Question | What the source found | Strength |
|---|---|---|
| Knee pain over 24 weeks (GAIT trial) | 1,583 people with symptomatic knee osteoarthritis received glucosamine, chondroitin sulfate, both, celecoxib or placebo; the supplements did not reduce pain significantly better than placebo overall. [2] An exploratory subgroup analysis suggested the combination may help moderate to severe pain. [2] | Mixed; subgroup result needs confirming |
| Joint structure over 2 years | Two large 2-year trials conflicted: an Australian one saw less joint-space narrowing with the combination, a US one saw no difference from placebo. [1] | Mixed |
| Overall comparison with other supplements | A 2018 review of 69 studies found glucosamine and chondroitin either ineffective or with small, arguably clinically unimportant effects. [3] | No good evidence of clinically important benefit |
| Other joints | NCCIH reports only a small amount of evidence outside the knee, and a hip trial found no benefit from glucosamine. [1] | Insufficient evidence |
Guidelines disagree. The NHS says GPs no longer prescribe them because there is no strong evidence, and NICE recommends they not be routinely offered. [4] NCCIH reports a 2019 US guideline strongly recommending against them for knee osteoarthritis, while a 2021 orthopaedic surgeons' guideline includes glucosamine among supplements that may help mild to moderate knee osteoarthritis, with a caution that evidence is inconsistent. [1]
The amounts above (1,500 mg of glucosamine and 1,200 mg of chondroitin sulfate daily for 24 weeks in GAIT) are study amounts, not advice. [2] We read no official intake level (RDA, AI or upper limit) for either substance. A clinician or pharmacist decides what, if anything, suits a person.
Side effects and cautions
- General: NCCIH says no major safety problems have been identified in large studies. [1] In GAIT, adverse events were mild, infrequent and similar across groups. [2]
- Warfarin and other blood thinners: NCCIH says both have been associated with increased bleeding risk in people taking warfarin. [1] The European Food Safety Authority concluded in 2011 that there is evidence of a risk of interaction between glucosamine and coumarin anticoagulants in some individuals, which could raise INR and lead to haemorrhage, though the level of risk could not be determined. [5] A case report described INR rising after a dose increase. [6] Do not stop or change a prescribed medicine on your own: talk to the prescriber or a pharmacist, and see medication interactions.
- Shellfish allergy: a study of Australian reports found that 71.85% of 366 adverse reports for glucosamine and chondroitin products were hypersensitivity reactions, though it was not clear whether those people had a known shellfish allergy. [7] The authors called for clear labelling for people prone to shellfish-related allergy. [7] If you have a shellfish allergy, ask an allergist or pharmacist before using these products, and check the label.
- Diabetes: glucosamine may raise blood glucose levels in some people. [1]
- Pregnancy and breastfeeding: little is known about safety. [1]
- Surgery: some supplements may increase bleeding risk or affect anesthesia; tell your surgical team well beforehand. [8] See supplements before surgery.
- Children, kidney and liver conditions: we found no source on these for glucosamine or chondroitin. Ask a clinician.
- Quality: what is on the label may not be what is in the product. [8] See quality testing and certifications.
In blends
Joint blends often add turmeric, MSM or collagen; see joint health formulas and bone, joint and sports recovery formulas. Compare labels using comparing supplement labels.Frequently asked questions
Does glucosamine work for knee arthritis?
NCCIH says it is still uncertain. [1] The GAIT trial found no significant overall pain benefit over placebo. [2]
Is glucosamine with chondroitin better than either alone?
Not clearly. NCCIH reports one combined analysis where each alone reduced pain but the combination did not; another trial saw an effect only for the combination on joint space. [1]
Is glucosamine safe with warfarin?
Not established. NCCIH links both to bleeding risk with warfarin, and EFSA found evidence of an interaction risk in some people. [1][5] Ask your prescriber or pharmacist.
Can I use glucosamine with a shellfish allergy?
Ask an allergist or pharmacist first. A study of Australian reports found many hypersensitivity reactions, though shellfish allergy status was unclear. [7]
Why doesn't the NHS prescribe them?
The NHS says there is no strong evidence they are effective as a treatment. [4]