Right to Refuse Medical Treatment
The Supreme Court has held that adults have the right to personal autonomy in matters relating to their own medical care. Adults, as long as they are competent to understand their decision, have the right to refuse medical treatment, even life-saving medical treatment, though a state may require clear and convincing evidence that a person wanted treatment ended before it allows termination. A state may restrict family members from terminating treatment for another, because this right belongs to each individual. The court has not extended this right to allow physician-assisted suicide.
https://www.justia.com/constitutional-law/docs/privacy-rights/