Dr Fuhrman is an M.D. who has fasted thousands of people for health problems. When Dr Oz (Oprah's doctor) has someone that is very obese, he send them to Dr Fuhrman. He will never do
Fasting on anyone for more than 50 days. This webpage on fasting has quotes about fasting by 19 different medical doctors.
You can check with your doctor but
Dr Fuhrman says that you should not fast if you are taking any medications. If you can stop taking them, then you can do the fast. Fasting can have very bad interactions with drugs.