Do I need a medical diploma to apply for an invention patent if I have invented something and a scheme that can treat chronic diseases?

This is unnecessary. If you find something and scheme that can treat chronic diseases, you can apply for a patent as long as you clearly write it down and declare it, whether you have a doctor's license or not. Because of these things, he will go through many layers of inspection and experiments, and finally judge whether your plan is effective. If it really works, it's all the same. You can also apply for ability, which are two different things.