That's a great question and unfortunately, there's no black and white answer. Until more research is done, the decision is really based on how frequently you can test and monitor if a change is happening.
Some research had suggested that glucosamine might worsen insulin resistance, which can contribute to increases in blood sugar in people with type 2 diabetes (which is also the type that cats have). However,other studies refute these findings and claim there is no notable affect.
So should diabetics use glucosamine? Consider the possible side effects (eg. digestive upset, headaches, drowsiness, bleeding tendencies) as well as the possibility that the blood sugar levels may increase. And know that close supervision is a must until you know how it affects your kitty.
If you decide to include glucosamine as part of your therapy, more frequent monitoring of blood glucose levels can show how your kitty's body is reacting. You would need to keep everything else consistent (food, dose, etc. so that you can isolate any changes).
As FYI - I have a dog that I've given Glucosamine to since he was 6 mos old. He's not diabetic, but we've never had a single side effect problem and now at 14 years old, 100 lbs....I believe it's made a huge difference in his life. It's a great supplement with many benefits, so if you can supervise and keep things consistent while you're trying it out - I'd give it a big thumbs up.
