A more thorough explanation:

The learned-intermediary doctrine is a principle that states that a prescription-drug manufacturer fulfills its duty to warn of a drug's potentially harmful effects by informing the prescribing physician, rather than the end-user, of those effects.

For example, if a patient is prescribed a medication for a certain condition, the manufacturer of the drug is not required to warn the patient directly about the potential side effects of the drug. Instead, the manufacturer is only required to provide the necessary information to the prescribing physician, who is considered the "learned intermediary" between the manufacturer and the patient.

This doctrine is based on the assumption that physicians are trained professionals who are capable of understanding the risks and benefits of a particular medication and can make informed decisions about whether to prescribe it to their patients. By providing the necessary information to the physician, the manufacturer is fulfilling its duty to warn about the potential risks associated with the drug.