(A)  Drug Abuse.  For purposes of this ground, drug abuse is defined as the “non-medical use of a substance listed in section 202 of the Controlled Substances Act, as amended (21 U.S.C. 802) which has not necessarily resulted in physical or psychological dependence.”[115]  Section 202 of the Controlled Substances Act is codified at 21 U.S.C. § 802, which lists hundreds of controlled substances, including marijuana, in five schedules. 

[115] 42 C.F.R. § 34.2(g) (as amended by May 31, 1991 interim rules, 56 Fed. Reg. 25000), reported on and reproduced in Interpreter Releases (June 3, 1991 and June 17, 1991).

Other

CONTROLLED SUBSTANCES - DRUG ABUSE AND ADDICTION
USCIS released a new medical examination form, dated 04/02/08, which includes specific questions on controlled substance use and addiction (Part 2, Q. 4), and has detailed instructions to physicians about completing these questions (page 6). Counsel must therefore prepare clients for medical exams and interviews by asking, "Have you ever smoked marijuana?" and "Are you in remission? Because if you are not in remission, you are inadmissible and have no waiver (unless you are a refugee or asylee doing AOS)." The HHS guidelines provide that an addict is someone who uses or has used a controlled substance for more than a single, experimental use. I-693 instructions: http://www.uscis.gov/files/form/I-693instr.pdf

Thanks to Deborah S. Smith.