Glucosamine: What It Does, Side Effects and Which to Buy

What to buy

Cosamin DS is our pick because it is on NSF/ANSI 173, which checks that each bottle holds what the label says. Three capsules a day give 1,500 mg glucosamine HCl and 1,200 mg chondroitin, the amounts the largest US trial used (Clegg 2006).

Want to spend less? Nature Made TripleFlex + D3 is USP Verified, at $0.32 a day, with 1,500 mg glucosamine and 800 mg chondroitin.

Where to go next

• Best glucosamine chondroitin supplement: the products we compared, with the trial results in detail.
• Third-party tested glucosamine: which ones are on a testing list, and the cost per day of each.

Does glucosamine work?

Results are mixed. In the largest US trial, neither glucosamine nor glucosamine with chondroitin clearly beat a placebo overall (Clegg 2006). The American College of Rheumatology advises against glucosamine for arthritis of the knee, hip or hand, and notes large placebo effects and a low risk of harm (2019).

Older trials of one prescription glucosamine sulfate found more benefit. NCCIH says most of those had a high risk of bias, were more than 20 years old and were paid for by the drug company. See the trial results.

Does glucosamine rebuild cartilage?

It has not been shown to. Two 3-year trials of 1,500 mg prescription glucosamine sulfate found that the space inside the knee joint narrowed less than on placebo, as seen on X-rays (Reginster 2001, Pavelka 2002). Both tested the same prescription product described above, and we found no trial that showed cartilage growing back.

Glucosamine sulfate or HCl?

Sulfate has more trials behind it, but many used one prescription brand. A Cochrane review found that brand beat placebo, while other glucosamine did not (Towheed 2005). The largest US trial used glucosamine HCl. The American College of Rheumatology says it is not clear how the form would change the result.

Both forms come in 1,500 mg a day products. Our tested list shows the form of each.

How long does glucosamine take to work?

The trials judged it after 6 months to 3 years. A few weeks is too soon to tell. If your joints feel no better after a few months, it is fair to stop.

Side effects and who should skip it

Side effects are usually mild: bloating, nausea, diarrhea or constipation (MedlinePlus). In trials, people on glucosamine reported side effects about as often as people on a placebo (Towheed 2005). Talk to your doctor first if any of these fit:

• Shellfish allergy: check the label. Many glucosamine labels say “contains shellfish”.
• Warfarin: case reports link glucosamine with warfarin to a higher INR, a sign of bleeding risk (Knudsen 2008). Ask before you start; your doctor may check your INR.
• Diabetes: some people show higher blood sugar on it (American College of Rheumatology), though a 6-week trial found no change in insulin resistance (Muniyappa 2006). If you have diabetes, check your blood sugar when you start.
• Glaucoma: a large UK study linked glucosamine use to higher eye pressure (Lehrer 2024).
• Pregnant or breastfeeding: safety is not known (NCCIH).

Glucosamine for dogs

A 2022 review of the dog and cat trials found glucosamine and chondroitin did not ease joint pain, and said they should no longer be recommended for it. Omega-3s did better. See joint supplements for dogs.

Questions people ask