The evidence behind glucosamine sulphate is very positive. A study published in the British Journal of Sports Medicine in 2003 investigated its effect on knee pain. Volunteers took either a daily glucosamine sulphate supplement or a dummy tablet for twelve weeks. 88% of the glucosamine sulphate group reported some degree of pain relief and improved function after twelve weeks, compared to just 17% taking the placebo.1
It is worth noting that many subjects who had noticed no difference in the first two months began improving in the third month of glucosamine sulphate supplementation. So if you are taking glucosamine, or considering it, don´t be discouraged if results take a few weeks.
I would recommend a daily dose of glucosamine if you take part in regular joint-intense exercise, even if you´re not suffering from knee pain. There are many glucosamine supplements on the market to choose from. Make sure you take at least 1500mg glucosamine sulphate daily. Some formulations contain other joint care ingredients (look out for vitamin D, bromelain and chondroitin) that can also be beneficial.
1Braham R et al; British Journal of Sports Medicine 2003, 37, 45-49