Non-citizens are removable from the United States for most drug convictions, except those that constitute “a single offense involving possession for one’s own use of 30 grams or less of marijuana.” The Board of Immigration Appeals (Board) has interpreted this “personal-use exception” to cover only offenses that, in addition to constituting “a single offense involving possession for one’s own use of 30 grams or less of marijuana,” are also the “least serious” drug offenses under the law of the state in which they were committed. The Fifth Circuit found no textual basis for the additional "least serious offense" criteria, and thus, declined to defer to the Board's interpretation.
The full text of Flores Esquivel v. Lynch can be found here: http://www.ca5.uscourts.gov/opinions/pub/13/13-60326-CV0.pdf