Try to be a little patient. Your subject was very general and it's quite possible the viewers (like me) don't have an answer for you or experience. I made a change to your subject line so hopefully it will draw some with knowledge/experience with this.
I think it is. First of all, glucosamine sulfate (the most commonly sold formula) is a salt. You don't want to overdo salts, especially in dogs with heart disease or renal issues.
Glucosamine sulfate may increase the risk of developing insulin resistance and could decrease the metabolic actions of insulin.
Although glucosamine and chondroitin sulfate are biochemically classed as carbohydrates (sugars), the body is not able to break them down into glucose, so these compounds do not raise blood sugar by providing an additional source of glucose. However, many factors can affect insulin secretion and blood glucose levels in diabetic patients, and we recommend that individuals with diabetes check their blood glucose levels frequently when initiating glucosamine into their regimen.
High dosages of glucosamine may cause gastric problems, nausea , diarrhea, indigestion, and heartburn. Glucosamine should be taken with meals to help avoid these problems.
The suggested dose for glucosamine for the "average" human, who weighs about 154 lbs, is somewhere in the range of 1,500 mg/day with chondroitin 1,200 mg/day. Most of our (standard size GSD) dogs weigh far less than that. I think it makes sense to give our dogs a reputable human grade supplement or a supplement from a very reputable veterinary provider willing to guarantee potency, (because otherwise, it's impossible to know what your dog is getting). So we're already double-dosing them at that potency, compared to humans. Granted, humans don't get hip dysplasia. So I think that the higher dosage is warranted. (Most of the bottles of Glucosamine for that I've looked at dogs suggest approx 1500ish mg for dogs over 75 lbs.) But much beyond that, I just don't think is a good idea. An owner can give Glucosamine snacks, kibble, supplements, etc. But at best, it's probably overkill (and a waste of money). At worst, it could be dangerous.
The thing is, Glucosamine has only been around approx 20 years. Long-term research isn't in. (There doesn't appear to be any long-term research on dogs, that I can find. So we'll have to rely on human research). Most dog owners I know have seen good to great results on a reasonable dosage. Why risk it?