Is it forbidden for a pharmacist to sell medications prescribed by a doctor in exchange for personal benefits from pharmaceutical companies?

The sin of deception falls upon the one who commits it, whether a doctor or not. The basic principle is that it is permissible to sell lawful medications. If a doctor deceives a specific patient by prescribing what they do not need, then it is obligatory to advise the patient and explain the situation to them, based on the Prophet's (peace and blessings be upon him) saying: "Religion is sincerity (or counsel)." And sincerity (or counsel) means intending the well-being of the advised person, freeing them from defects, and purifying them from deception.