What is the ruling on substituting one medication for another with the same active ingredient and concentration in a pharmacy, without the patient's or doctor's permission?

If the purpose of dispensing medication is to recommend it to the buyer for purchase, then if the medication prescribed in the recipe is available, it is not permissible for the pharmacist to give the buyer an alternative or equivalent; because selecting the appropriate medication is the prerogative of the treating physician.

However, if the prescribed medication is not available, it is not permissible to sell a substitute without informing the buyer so that they can consult their physician. The contract is made for the prescribed item, and it is not permissible to sell something else without their knowledge. This is especially true if the price of the substitute is higher.