Montana Title 46. Criminal Procedure § 46-14-213. Psychiatric or psychological testimony upon trial

(1) Upon trial, any psychiatrist, licensed clinical psychologist, or advanced practice registered nurse who reported under 46-14-202 or 46-14-206 may be called as a witness by the prosecutor or by the defense. Both the prosecution and the defense may summon any other qualified psychiatrist, licensed clinical psychologist, or advanced practice registered nurse to testify, but only a person who has examined the defendant is competent to testify to an expert opinion with respect to the mental condition of the defendant, as distinguished from the validity of the procedure followed by or the general scientific propositions stated by another witness.

(2) When a psychiatrist, licensed clinical psychologist, or advanced practice registered nurse who has examined the defendant testifies concerning the defendant's mental condition, the psychiatrist, licensed clinical psychologist, or advanced practice registered nurse may make a statement as to the nature of the examination and the medical or psychological diagnosis of the mental condition of the defendant. The expert may make any explanation reasonably serving to clarify the expert's examination and diagnosis, and the expert may be cross-examined as to any matter bearing on the expert's competency or credibility or the validity of the expert's examination or medical or psychological diagnosis. A psychiatrist, licensed clinical psychologist, or advanced practice registered nurse may not offer an opinion to the jury on the ultimate issue of whether the defendant did or did not have a particular state of mind that is an element of the offense charged.