Texas Health and Safety Code - HEALTH & SAFETY § 433.089. Immunity

(a) A person is not excused from attending and testifying or producing documentary evidence before the department or in obedience to the department's subpoena, whether signed by the commissioner or the commissioner's designee, or in a cause or proceeding based on or growing out of an alleged violation of this chapter, on the ground that the required testimony or evidence may tend to incriminate the person or subject the person to penalty or forfeiture.

(b) A person may not be prosecuted or subjected to a penalty or forfeiture for or because of a transaction or matter concerning which the person is compelled to testify or produce evidence after having claimed a privilege against self-incrimination.

(c) The person testifying under this section is not exempt from prosecution and punishment for perjury committed in that testimony.