Drug convictions and Immigration Laws are very complicated and require careful analysis. The good news is that a person cannot be deported from the U.S. for Possession of Marijuana as long as the amount does not exceed 30 grams. However, a conviction for any other type of marijuana offense other than simple possession of 30 grams or less requires mandatory deportation.
INA § 237(a)(2)(B)(i) provides as follows:
Any alien who at time after admission has been convicted of a violation of (or a conspiracy or attempt to violate) any law or regulation of a State, the United States, or a foreign country relating to a controlled substance (as defined in section 102 of the Controlled Substances Act (21 U.S.C. 802), other than a single offense involving possession for one’s own use of thirty grams or less of marijuana is deportable.
Visa Lawyer Blog

