Glucosamine is probably the most widely used joint health supplement on the planet. Walk into any pharmacy and you’ll find shelves of it, usually combined with chondroitin or non-denatured type II collagen. Surveys suggest that around 59% of people who’ve tried complementary therapies have taken glucosamine at some point.

But here’s the question that matters: does it actually work? I’ve gone through the clinical research, and the answer is more complicated than the marketing suggests. Some people swear by it. The scientific evidence is decidedly mixed. Let me walk you through what we actually know.

What is glucosamine?

Glucosamine is an amino sugar that your body produces naturally. It’s found throughout your connective tissues, cartilage, ligaments, and tendons, where it helps maintain structure and flexibility.

The supplement form is typically extracted from shellfish shells (shrimp, crab, lobster), though vegetarian versions made from fermented corn exist. The idea behind supplementation is straightforward: if glucosamine is a building block for cartilage, taking more of it might help repair damaged joints.

Whether that logic holds up in practice is another matter entirely.

Laboratory studies have shown glucosamine has antioxidant and anti-inflammatory properties [1]. That’s encouraging, but what happens in a petri dish doesn’t always translate to what happens in an actual human body.

When should you take glucosamine? What dose?

Most clinical trials have used 1500mg daily, either as a single dose or split into three 500mg doses throughout the day. Taking it with food helps reduce stomach upset.

Interestingly, there’s some evidence that multiple smaller doses may work better than one large dose. One analysis found that splitting the dose provided greater pain relief than taking 1500mg all at once [2]. The reasons aren’t entirely clear, but it might relate to how the body absorbs and processes the compound.

What the research shows: 5 potential benefits

I should be upfront here: glucosamine research is frustrating. Some trials show benefits, others show nothing. The quality varies enormously. Here’s my honest assessment of where things stand.

1. Osteoarthritis pain relief

Osteoarthritis is the main reason people take glucosamine, so let’s start here.

A meta-analysis of 18 randomised controlled trials found that oral glucosamine did help with pain compared to placebo, as measured by visual analogue pain scores and the Japanese knee osteoarthritis scale [3]. However, the effect was described as “limited.”

Another analysis of 17 trials with 2,212 participants came to a similar conclusion: there may be a “small to moderate effect” on pain, but glucosamine doesn’t appear to slow down actual joint degeneration or prevent narrowing of the joint space [2].

My take: if you’re hoping glucosamine will rebuild your cartilage or reverse arthritis, the evidence doesn’t support that. But for pain management? Some people do seem to get modest relief. Whether that relief is worth the cost of supplements is a personal calculation.

The NHS notes that current evidence doesn’t strongly support glucosamine for osteoarthritis, though they acknowledge some people report benefits [4].

2. Temporomandibular joint dysfunction

Temporomandibular disorder (TMD) affects the jaw joint and surrounding muscles. It’s surprisingly common, affecting somewhere between 21% and 50% of the population, with women more affected than men.

A meta-analysis of three randomised controlled trials found that glucosamine combined with chondroitin sulfate improved maximum mouth opening in TMD patients [5]. The pain reduction was comparable to the analgesic tramadol, which is interesting.

Three trials isn’t much to go on, so I’d call this preliminary. But if you have TMD and standard treatments aren’t working, it might be worth discussing with your dentist or doctor.

3. Colorectal cancer risk reduction

This one caught my attention. A cohort study following 113,067 participants found that glucosamine users had about 17% lower risk of developing colorectal cancer compared to non-users [6]. Oddly, the association was strongest with short-term use (less than two years) rather than long-term supplementation.

The proposed mechanism relates to glucosamine’s anti-inflammatory effects. It may inhibit NF-kappaB (an inflammatory transcription factor) and reduce levels of pro-inflammatory molecules like TNF-alpha and interleukin-6.

I should be clear: this is observational data, not proof of cause and effect. People who take glucosamine might differ from non-users in ways that affect cancer risk. We’d need randomised controlled trials to know whether glucosamine actually prevents colorectal cancer, and those don’t exist yet.

4. Vascular endothelial function

Your blood vessel lining (endothelium) regulates blood pressure, clotting, and inflammation. When it stops working properly, you’re at higher risk for hypertension, coronary artery disease, and other cardiovascular problems.

A controlled study of 39 male volunteers found that four weeks of glucosamine supplementation improved flow-mediated vasodilation, a measure of how well blood vessels relax [7]. The supplement also improved markers of oxidative stress, including the ratio of reduced to oxidised glutathione inside red blood cells.

This is a small study, but the proposed mechanism is plausible. Glucosamine may help blood vessels by reducing oxidative damage. More research is needed.

5. Lung cancer risk reduction

A follow-up study of 76,904 participants found that long-term glucosamine use (four or more times per week for over three years) was associated with lower lung cancer risk, specifically for adenocarcinoma [8].

Again, this is observational data with all the limitations that implies. Correlation doesn’t equal causation. But it’s consistent with the anti-inflammatory hypothesis: chronic inflammation contributes to cancer development, and glucosamine may have anti-inflammatory effects.

Does glucosamine affect blood sugar?

Since glucosamine is technically a sugar derivative, there’s been concern it might worsen blood sugar control or contribute to insulin resistance. This has been demonstrated in animal studies.

A double-blind, placebo-controlled study followed 407 middle-aged women with BMI of 27 or higher for 6.5 years [9]. The results were reassuring: glucosamine didn’t affect average glycated haemoglobin (HbA1c) levels and didn’t increase the risk of new diabetes diagnoses in people with normal baseline levels.

For people who already had elevated HbA1c at the start, there was a trend toward higher values with glucosamine use, but it wasn’t statistically significant.

My interpretation: if you don’t have diabetes, glucosamine probably won’t cause problems with blood sugar. If you do have diabetes, you should monitor your levels more closely and discuss supplementation with your doctor.

Side effects of glucosamine

Glucosamine is generally well tolerated in healthy adults. The most common side effects involve the digestive system:

Nausea
Heartburn
Diarrhoea
Indigestion

Taking it with food usually helps. Less common side effects include drowsiness, skin reactions, and headache.

According to the Mayo Clinic, glucosamine is likely safe for most people when taken at recommended doses, though they note the evidence for effectiveness is mixed [10].

Safety precautions (11 contraindications)

Blood sugar concerns: While not definitively proven, glucosamine may affect blood sugar and blood pressure in some individuals. If you’re taking medications for these conditions, monitor your levels carefully.
Shellfish allergy: Most glucosamine supplements are derived from shrimp and crab shells. If you’re allergic to shellfish, look for vegetarian alternatives made from fermented corn or fungi, or avoid glucosamine entirely.
Blood thinning effects: Glucosamine may have mild anticoagulant properties. If you have a bleeding disorder, take blood thinners like warfarin, or have surgery scheduled, stop glucosamine at least two weeks beforehand and inform your surgeon.
Pregnancy and breastfeeding: There’s insufficient safety data for pregnant or nursing women. The general advice is to avoid it during these periods.
Asthma: Some reports suggest glucosamine may trigger or worsen asthma symptoms in susceptible individuals.
Sodium and potassium content: Glucosamine sulfate formulations often contain significant amounts of sodium or potassium as stabilisers. This matters if you’re on a sodium-restricted diet or taking potassium-sparing diuretics.
Chemotherapy drugs: Don’t combine glucosamine with certain cancer medications including doxorubicin, etoposide, and teniposide. It may interfere with their effectiveness.
Glaucoma or elevated intraocular pressure: A small study suggested glucosamine might raise intraocular pressure [11]. If you have glaucoma or are at risk, discuss this with your ophthalmologist.
Paracetamol interactions: There’s concern that glucosamine may reduce the effectiveness of paracetamol (acetaminophen). If you rely on paracetamol for pain relief, this could matter.
Chronic liver disease: There have been isolated case reports of elevated liver enzymes (AST) in people with pre-existing liver conditions who took glucosamine [12].
Cholestasis risk: Rare cases of drug-induced cholestasis (blocked bile flow) have been reported with glucosamine plus chondroitin, even in people without prior liver disease [13].

Available forms of glucosamine

You’ll find several forms on pharmacy shelves:

Glucosamine hydrochloride: Contains more glucosamine per gram than the sulfate form
Glucosamine sulfate: Usually stabilised with potassium chloride; this is the form used in most European clinical trials
Crystalline glucosamine sulfate: A patented form with more consistent quality control
N-acetyl glucosamine: A different derivative that doesn’t appear to have the same clinical activity and is rarely recommended

The bottom line

Glucosamine is one of those supplements where the marketing has outpaced the science. It won’t rebuild your cartilage or reverse arthritis. The evidence for slowing joint degeneration simply isn’t there.

That said, some people do report meaningful pain relief, and the safety profile is reasonable for most users. If you have osteoarthritis and want to try it, a three-month trial at 1500mg daily (ideally split into smaller doses) is a reasonable approach. If you don’t notice any improvement by then, it’s probably not working for you.

One important note: glucosamine isn’t appropriate for all joint pain. Conditions like rheumatoid arthritis, gout, and joint infections require different treatments. If you have unexplained joint pain lasting more than a week, see a doctor to get a proper diagnosis before self-treating with supplements.

Benefits and side effects of chondroitin - often taken alongside glucosamine
Health foods beneficial for osteoarthritis
Benefits and side effects of cat’s claw - another supplement used for joint pain

References

Velusami CC, et al. Safety evaluation of turmeric polysaccharide extract. BMC Complement Altern Med. 2016;16:145. https://www.ncbi.nlm.nih.gov/pubmed/27012765
Ogata T, et al. Effects of glucosamine in patients with osteoarthritis of the knee: a systematic review and meta-analysis. Clin Rheumatol. 2019;38(9):2413-2426. https://www.ncbi.nlm.nih.gov/pubmed/30566740
Zhu X, et al. Effectiveness and safety of glucosamine and chondroitin for the treatment of osteoarthritis: a meta-analysis of randomized controlled trials. J Orthop Surg Res. 2018;13(1):170. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6097075/
NHS. Glucosamine. https://www.nhs.uk/conditions/glucosamine/
Mitsimponas N, et al. Chondroitin sulfate and glucosamine in temporomandibular joint disorders: A systematic review and meta-analysis. J Oral Rehabil. 2022;49(9):923-934. https://pubmed.ncbi.nlm.nih.gov/35588467/
Kantor ED, et al. Use of glucosamine and chondroitin supplements and risk of colorectal cancer. Cancer Causes Control. 2018;29(1):85-94. https://www.ncbi.nlm.nih.gov/pubmed/29411204
Dalirfardouei R, et al. Molecular mechanisms and biomedical applications of glucosamine as a potential multifunctional therapeutic agent. Life Sci. 2016;167:58-69. https://www.ncbi.nlm.nih.gov/pubmed/29151484
Brasky TM, et al. Use of glucosamine and chondroitin and lung cancer risk in the VITamins And Lifestyle (VITAL) cohort. Cancer Causes Control. 2011;22(9):1333-1342. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3175750/
de Abreu DC, et al. Effect of glucosamine supplementation for 6.5 years on glycated hemoglobin in a randomized controlled trial. Br J Sports Med. 2017;51(16):1237-1242. https://www.ncbi.nlm.nih.gov/pubmed/28011309
Mayo Clinic. Glucosamine. https://www.mayoclinic.org/drugs-supplements-glucosamine/art-20362874
Esfandiari H, et al. Can glucosamine cause glaucoma? J Glaucoma. 2017;26(2):e55-e56. https://www.ncbi.nlm.nih.gov/pubmed/27768119
Cerda C, et al. Severe hepatotoxicity associated with glucosamine: a case report. Am J Case Rep. 2013;14:252-256. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3752575/
Yang Y, et al. Drug-induced cholestasis associated with glucosamine and chondroitin sulfate combination. Case Rep Med. 2015;2015:587249. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4621470/