§ 21.15 (C)
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(C) Compared to Inadmissibility Ground. Unlike the inadmissibility ground, this ground does not forgive those who have been clean for three years. However, this ground requires that the abuse or addiction must have occurred or existed “after admission.” Unlike the inadmissibility ground, simply “admitting” drug abuse or addiction to an immigration official or doctor in the course of a physical examination for immigration purposes is arguably insufficient to sustain this ground. In deportation proceedings the DHS bears the burden of proof. Noncitizens can therefore contest deportability and submit evidence from an independent physician on the issue of drug abuse or addiction. Arguably the DHS must submit proof that the noncitizen was found to be an addict by a judicial body and ordered to participate in a rehabilitation program. The DHS may also need to present evidence of multiple instances of drug use.
 See § § 17.5-17.8, supra.
 See Matter of FSC, 8 I. & N. Dec. 108 (BIA 1958) (a noncitizen’s admission of addiction was held to be not sufficient when contradicted by two physician’s opinions and repudiated by the alien).
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.