Imaam Sadi (rahimahullaah) said: Medical Remedy Is Founded Upon Three Fundamental Affairs:
Preservation of health through engagement in beneficial activities;
Protection of (oneself) from harmful things;
To repel those harmful things the body is exposed to.
All medical remedies revolve around these (above) three affairs. The Qur’aan has informed us about this, regarding the preservation of health and protection from harmful things.
Allaah (The Most High) said:
‘’And eat and drink but waste not by extravagance’’ [Surah Araaf; Ayah: 31]
So Allaah (The Most High) commanded (us) with that eating and drinking, without which the bodies cannot be wholesome; and this indicates that food and drink are estimated in accordance with what is either beneficial or harmful to the human being at every instance and in every situation. Allaah has forbidden excessiveness in (consumption of food and drink), and that can either be an increase in much food or beverages, or a mixture of both. This (forbiddance from excessive consumption of food and drink) is a protection from all that harms the human being. And when it is the case that it is forbidden to (partake) in that essential nourishment from food and drink to a level that injures and harms the body, then how about (harm and injury to the body) with other than (food and drink)?!
Likewise, Allaah made it permissible for an ill person to perform Tayammum if usage of water will harm him; and this is a protection for him from all that is harmful. And Allaah made it permissible for the Muhrim(1) with an ailment in his scalp (necessitating shaving) to shave his hair and pay a Fidyah (i.e. a ransom-which is to either to observe three days of fasting or offer a sacrifice of one sheep). This is done in order to remove and eliminate that which may be harmful to the body, then how about that which has greater harm than this?!
And Allaah has forbidden that the body is made to have contact with what may lead to its destruction, and this includes utilization of all that is harmful to the human being of foodstuffs and medicines……