The difference between Synovi G3 and G4 is that the G3 is for healthy and active dogs, but the G4 is used to help maintain joint health in aging or old dogs. Synovi G3 soft chews for dogs are to support joint functionality and flexibility. The G4 also exists to support joint function in dogs. However, there is a major difference between them. The G3 is consumed by healthy dogs. A healthy dog is given G3 soft chews as a supplement so that it can maintain its joint strength. The G4 tablets, on the other hand, help support joint cartilage in weak, old, or aging dogs. These tablets promote joint health. Hence, even when they are getting older, the dogs will not feel any difficulty in moving about.