What we found

Three products weren't up to scratch:

• Nutralife High Potency Joint Care Arthritis Formula with Glucosamine and Chondroitin
• Good Health Joint Zone Glucosamine
• Chondroitin; and Bioorganics Joint Formula Glucosamine 750 + Chondroitin 400

These had only 86 to 90 percent of the amount of glucosamine stated on the label.

No products had more than 100 percent of the label claim.

Our test reinforces the argument that dietary supplements need to be regulated to ensure consumers are getting high-quality products that meet their claims.

Test criteria

Glucosamine and other dietary supplements are covered by the Dietary Supplements Regulations. The regulations require proper labelling, but there's no auditing of a manufacturer's processes.

Across the Tasman, there are more stringent regulations. According to the Therapeutic Goods Administration's manufacturing regulations, products must have between 92.5 percent and 107.5 percent of the active ingredient claimed on the label. We used these criteria for our test.

For details of all the products we tested, see the Test results.

Price and dose

Depending on the amount of glucosamine in each tablet you need to take one or two tablets each day to get the recommended effective dose.

There's a big range of prices. Blackmores Glucosamine 1500 was the cheapest in our survey - it costs 46c per day. Bioorganics Joint Formula Glucosamine 750 + Chondroitin 400 cost more than double that - $1.22 per day. It's an even bigger rip-off because the Bioorganics product contained only 87 percent of the glucosamine claimed on the label.

Confusing labels

The labels on these supplements can be very confusing because glucosamine comes in different chemical forms that contain different amounts of "actual" glucosamine. It can make a big difference to how much of the active ingredient you're taking.

1000mg of glucosamine hydrochloride is equivalent to 830mg of glucosamine. 1000mg of glucosamine sulphate is equivalent to 785mg. 1000mg of glucosamine sulphate potassium chloride complex delivers only 590mg of glucosamine.

Some brands leave you to decipher the small print to find out which chemical form, and how much glucosamine, you're getting.