Massachusetts General Laws Part IV. Crimes, Punishments and Proceedings in Criminal Cases (Ch. 263-280) Ch. 263, § 5A

A person held in custody at a police station or other place of detention, charged with operating a motor vehicle while under the influence of intoxicating liquor, shall have the right, at his request and at his expense, to be examined immediately by a physician selected by him. The police official in charge of such station or place of detention, or his designee, shall inform him of such right immediately upon being booked, and shall afford him a reasonable opportunity to exercise it. Such person shall, immediately upon being booked, be given a copy of this section unless such a copy is posted in the police station or other place of detention in a conspicuous place to which such person has access.