Reference: Fataawa al-Lajnah ad-Daa.imah lil-Buhooth al-‘Ilmiyyah wal-Iftaa. – Question 11, Fatwa No.6908
al-Fataawa al-Muta’alliqah bit-Tibb wa Ahkaam al-Mardhaa – Pages 174-175
Question: Sometimes a doctor needs to lie to the patient, particularly when his condition does not permit him to comprehend the [full extent of the] situation he is in, so [in this case] has the doctor sinned?
Response: It is permissible to lie to him (the patient) so long as the lie benefits him and does not harm him nor others. If, however, the doctor was able to use suggestive words instead of blatantly lying, then that is safer and better.
And with Allaah lies all success and may Allaah send prayers and salutations upon our Prophet Muhammad (sal-Allaahu `alayhi wa sallam) and his family and his companions.