Tennessee Code Title 39. Criminal Offenses § 39-11-203

(a) A defense to prosecution for an offense in this title is so labeled by the phrase: “It is a defense to prosecution under...that...”

(b) The state is not required to negate the existence of a defense in the charge alleging commission of the offense.

(c) The issue of the existence of a defense is not submitted to the jury unless it is fairly raised by the proof.

(d) If the issue of the existence of a defense is submitted to the jury, the court shall instruct the jury that any reasonable doubt on the issue requires the defendant to be acquitted.