Any qualified mental health professional, upon being authorized by the administrator of the treatment facility having custody of the subject, may provide appropriate medical treatment for the subject while in custody, except that a subject shall not be subjected to such quantities of medication or other treatment within such period of time prior to any hearing held under the Nebraska Mental Health Commitment Act or the Sex Offender Commitment Act or, for a subject who is domiciled in Indian country and committed for treatment as provided in section 71-964, a hearing held under the equivalent tribal law, as will substantially impair his or her ability to assist in his or her defense at such hearing.