Here is an interesting couple of paragraphs from a US Court of Appeals case, Douglas v. Dobbs, Key, And District Attorney's Office For The Twelfth Judicial District (US CA, 10th), on privacy in relation to health care records:

The scope of personal matters protected by a right to privacy has never been fully defined. Supreme Court decisions "make it clear that the right has some extension to activities relating to marriage, procreation, contraception, family relationships, and child rearing and education." Roe v. Wade... Because privacy regarding matters of health is closely intertwined with the activities afforded protection by the Supreme Court, we have held that "there is a constitutional right to privacy that protects an individual from the disclosure of information concerning a person's health." ... We have previously applied this right in the context of an employer's search of an employee's medical records, Lankford v. City of Hobart...and in the context of a government official's disclosure of a person's HIV status. A.L.A. v. West Valley City...

Although we have not extended the "zone of privacy" to include a person's prescription records, we have no difficulty concluding that protection of a right to privacy in a person's prescription drug records, which contain intimate facts of a personal nature, is sufficiently similar to other areas already protected within the ambit of privacy. See, e.g., Griswold v. Connecticut.... Information contained in prescription records not only may reveal other facts about what illnesses a person has, but may reveal information relating to procreation ­ whether a woman is taking fertility medication for example ­ as well as information relating to contraception. See Eisenstadt v. Baird...("If the right of privacy means anything, it is the right of the individual, married or single, to be free from unwarranted governmental intrusion into matters so fundamentally affecting a person as the decision whether to bear or beget a child."); Stidham v. Peace Officer Stds. & Training...(providing that disclosed information "must be highly personal or intimate" in order to receive constitutional privacy protection); Doe v. Southeastern Pennsylvania Transportation Authority...(holding that "[a]n individual using prescription drugs has a right to expect that such information will customarily remain private."). Thus, it seems clear that privacy in prescription records falls within a protected "zone of privacy" and is thus protected as a personal right either "fundamental" to or "implicit in the concept of ordered liberty."...