Which document allows an individual to dictate medical choices if they are unable to express their wishes?

The correct answer is a living will. This document is specifically designed to outline an individual's preferences regarding medical treatments and interventions in situations where they are unable to communicate their wishes due to illness or incapacitation. A living will typically addresses scenarios such as the use of life-sustaining measures, resuscitation efforts, and other critical care decisions.

In this context, the living will serves as a guide for healthcare providers and family members, ensuring that the individual's values and preferences regarding end-of-life care are respected even when they cannot voice those decisions themselves.

While a regular will deals with the distribution of a person's estate after death and a Power of Attorney grants someone authority to make financial or legal decisions on behalf of another person, neither specifically addresses medical choices. A healthcare proxy, while closer in function, designates an individual to make medical decisions on someone’s behalf, rather than providing the direct expression of wishes that a living will offers.