(a) Except as authorized by this chapter, a person commits an offense if the person knowingly possesses a controlled substance listed in Penalty Group 2-A, unless the person obtained the substance directly from or under a valid prescription or order of a practitioner acting in the course of professional practice.
(b) An offense under this section is:
(1) a Class B misdemeanor if the amount of the controlled substance possessed is, by aggregate weight, including adulterants or dilutants, two ounces or less;
(2) a Class A misdemeanor if the amount of the controlled substance possessed is, by aggregate weight, including adulterants or dilutants, four ounces or less but more than two ounces;
(3) a state jail felony if the amount of the controlled substance possessed is, by aggregate weight, including adulterants or dilutants, five pounds or less but more than four ounces;
(4) a felony of the third degree if the amount of the controlled substance possessed is, by aggregate weight, including adulterants or dilutants, 50 pounds or less but more than 5 pounds;
(5) a felony of the second degree if the amount of the controlled substance possessed is, by aggregate weight, including adulterants or dilutants, 2,000 pounds or less but more than 50 pounds; and
(6) a felony of the first degree punishable by imprisonment in the Texas Department of Criminal Justice for life or for a term of not more than 99 years or less than 5 years, and a fine not to exceed $50,000, if the amount of the controlled substance possessed is, by aggregate weight, including adulterants or dilutants, more than 2,000 pounds.

(c) It is a defense to prosecution for an offense punishable under Subsection (b)(1) or (2) that the actor:
(1) was the first person to request emergency medical assistance in response to the possible overdose of another person and:
(A) made the request for medical assistance during an ongoing medical emergency;
(B) remained on the scene until the medical assistance arrived; and
(C) cooperated with medical assistance and law enforcement personnel; or
(2) was the victim of a possible overdose for which emergency medical assistance was requested, by the actor or by another person, during an ongoing medical emergency.
(d) The defense to prosecution provided by Subsection (c) is not available if:
(1) at the time the request for emergency medical assistance was made:
(A) a peace officer was in the process of arresting the actor or executing a search warrant describing the actor or the place from which the request for medical assistance was made; or
(B) the actor is committing another offense, other than an offense punishable under § 481.115(b), 481.1151(b)(1), 481.116(b), 481.117(b), 481.118(b), or 481.121(b)(1) or (2), or an offense under § 481.119(b), 481.125(a), 483.041(a), or 485.031(a);
(2) the actor has been previously convicted of or placed on deferred adjudication community supervision for an offense under this chapter or Chapter 483 or 485;
(3) the actor was acquitted in a previous proceeding in which the actor successfully established the defense under that subsection or § 481.115(g), 481.1151(c), 481.116(f), 481.117(f), 481.118(f), 481.119(c), 481.121(c), 481.125(g), 483.041(e), or 485.031(c); or
(4) at any time during the 18-month period preceding the date of the commission of the instant offense, the actor requested emergency medical assistance in response to the possible overdose of the actor or another person.
(e) The defense to prosecution provided by Subsection (c) does not preclude the admission of evidence obtained by law enforcement resulting from the request for emergency medical assistance if that evidence pertains to an offense for which the defense described by Subsection (c) is not available.