Q. Excessive drooling when left alone 6 mths old and just started this
A. Excessive drooling like this may be a stress response. If this is happening when you are leaving him alone (and you are sure he isn't getting into anything) which may cause it. Based on his age this is a typical time we start to see behavioral issues, he may be suffering from separation anxiety. Dogs that suffer from it may be destructive, howl & bark, go to the bathroom in the house even though they are potty trained, and in extreme cases can work themselves up to the point they drool or even ill. Without knowing more information about the symptoms and behavior it is really hard to comment that this is the problem. I would recommend that once any health reasons have been ruled out, you speak to very experienced trainer. You will need professional help and guidance to work through this issue and give you the tools to be effective in helping him through this. This is imperative that be it addressed now. Over time, the behavior re-enforces itself and it gets worse and harder to treat.