Answer
Wa `alaykum As-Salamu waRahmatullahi wa Barakatuh.
In the Name of Allah, Most Gracious, Most Merciful.
All praise and thanks are due to Allah, and peace and blessings be upon His Messenger.
In this fatwa:
If telling the truth about the patient’s health conditions seems necessary for him to know his disease to help on caring about himself and avoiding certain foods or to take certain medicines, it is obligatory to do so.
Answering your question, Dr. Mohammad S. Alrahawan, Associate Professor at the department of Islamic Studies in English, Al-Azhar University, Egypt, states:
Telling the truth about patients’ health conditions depends on the case and status of the patient. If it seems necessary for him to know his disease to help on caring about himself and avoiding certain foods or to take certain medicines, it is obligatory to do so. This is to keep him safe.
But if it does not make a difference, it is recommended not to tell him the truth about his disease. The physician must make his patients hopeful about the future.
Allah Almighty knows best.