Hawzah News Agency – Q: Since some physicians are not aware of Islamic laws, should the patient obey a physician’s order if he forbids fasting?
A: If the physician’s statement makes the patient certain that fasting is harmful for him or he fears of harm in fasting — either on the basis of his statements or on some other reasonable grounds — then it is not obligatory for him to fast.
Source: https://www.leader.ir/en/book/32/Practical-Laws-of-Islam