Ibn Al-Qayyim (rahimahu Allah) says: The Qur’an is the complete healing for all mental, spiritual and physical diseases, all diseases of this world and the Hereafter. But not everyone is guided to use it for the purpose of healing. If the sick person uses the Qur’an for healing in the proper way, and applies it to his disease with sincerity, faith, complete acceptance and firm conviction, fulfilling all its conditions, then no disease can resist it. How can disease resist the words of the Lord of heaven and earth which, if He had revealed it to the mountains they would have crumbled and if He had revealed it to the earth it would have broken it apart? There is no sickness, spiritual or physical, but in the Qur’an there is that which indicates its remedy, its cause and how to protect against it for those who are blessed with understanding of His Book. 

[Zaad al-Ma’aad, 4/352]