Glucosamine sulphate is a dietary supplement — a salt of glucosamine, an amino sugar that is a building block of cartilage — widely taken for joint health, particularly osteoarthritis of the knee. Athletes and older adults use it in the hope that supplying the raw material will help rebuild damaged cartilage and ease pain and stiffness. Clinical trials give a mixed verdict: some show modest symptom relief, others no better than placebo, and it does not convincingly regrow cartilage on imaging. It is generally well tolerated, though people with shellfish allergy should note that most glucosamine is derived from crustacean shells. As with many joint supplements, enthusiastic marketing runs well ahead of the evidence.