A more thorough explanation:

A learned intermediary is a person who acts as a mediator or go-between in the chain of distribution from the manufacturer to the consumer and who knows the risks of the product. This person is responsible for informing the consumer about the potential risks associated with the product.

For example, in the case of prescription drugs, the learned intermediary is typically the prescribing physician. The physician is responsible for informing the patient about the potential risks and benefits of the drug before prescribing it. The patient relies on the physician's expertise and knowledge to make an informed decision about whether to take the drug.

In products liability cases, the learned intermediary defense is often used to argue that the manufacturer is not liable for any harm caused by the product because the intermediary (such as the physician) failed to adequately warn the consumer about the risks.