Mont. Code Ann. § 46-14-217

A statement made for the purposes of psychiatric or psychological examination or treatment provided for in this section by a person subjected to examination or treatment is not admissible in evidence against the person at trial on any issue other than that of the person's mental condition. It is admissible on the issue of the person's mental condition, whether or not it would otherwise be considered a privileged communication, only when and after the defendant presents evidence that due to a mental disease or disorder the defendant did not have a particular state of mind that is an element of the offense charged.