This should help:
18-12-106. Prohibited use of weapons.
(1) A person commits a class 2 misdemeanor if.............................
(d) The person has in his or her possession a firearm while the person is under the influence of intoxicating liquor or of a controlled substance, as defined in section 12-22-303 (7), C.R.S. Possession of a permit issued under section 18-12-105.1, as it existed prior to its repeal, or possession of a permit or a temporary emergency permit issued pursuant to part 2 of this article is no defense to a violation of this subsection (1).
definitions controlled substances
7) "Controlled substance" shall have the same meaning as in section 18-18-102 (5), C.R.S.
(7.5) (a) "Controlled substance analog" means a substance the chemical structure of which is substantially similar to the chemical structure of a controlled substance in schedule I or II and:
(I) Which has a stimulant, depressant, or hallucinogenic effect on the central nervous system substantially similar to the stimulant, depressant, or hallucinogenic effect on the central nervous system of a controlled substance included in schedule I or II; or
(II) With respect to a particular individual, which that individual represents or intends to have a stimulant, depressant, or hallucinogenic effect on the central nervous system substantially similar to the stimulant, depressant, or hallucinogenic effect on the central nervous system of a controlled substance included in schedule I or II.
(b) "Controlled substance analog" does not include:
(I) A controlled substance;
(II) Any substance for which there is an approved new drug application;
(III) With respect to a particular person, any substance, if an exemption is in effect for investigational use, for that person, under section 505 of the "Federal Food, Drug, and Cosmetic Act", 21 U.S.C. sec. 355, as amended, to the extent that conduct with respect to the substance is pursuant to the exemption; or
(IV) Any substance to the extent not intended for human consumption before such an exemption takes effect with respect to the substance.
intoxication definition: 18-1-804. Intoxication.
(4) "Intoxication", as used in this section means a disturbance of mental or physical capacities resulting from the introduction of any substance into the body.
(5) "Self-induced intoxication" means intoxication caused by substances which the defendant knows or ought to know have the tendency to cause intoxication and which he knowingly introduced or allowed to be introduced into his body, unless they were introduced pursuant to medical advice or under circumstances that would afford a defense to a charge of crime.