Glucosamine can be a wonderful joint support supplement. There is some research claiming that it does not work but try telling that to the millions of people who swear by it. My opinion is that each person has the potential to respond differently to it, just like all people have the potential to respond differently to medications. You will never know until you try it.
I highly recommend a trial period of 4 weeks if you are thinking about using it. It has no know toxicity and is considered very safe. Most glucosamine is derived from shellfish, so if you have a severe shellfish allergy you may want to be careful.
The suggest dose is 1500mg per day. This is usually divided up into three 500mg doses over the course of the day. 1500mg seems to be the magic number and is the dose most likely to create beneficial results.