A pure dose of the hallucinogenic drug LSD is so small that it must be sold to retail customers in a "carrier" created by dissolving pure LSD and, inter alia, spraying the resulting solution on paper. That paper is then cut into "one-dose" squares, which users swallow, lick, or drop into a beverage to release the drug. Petitioners were convicted in the District Court of selling 10 sheets (1,000 doses) of blotter paper containing LSD, in violation of 21 U.S.C. 841(a). Section 841(b)(1)(B) calls for a 5-year mandatory minimum sentence for the offense of distributing more than one gram of "a mixture or substance containing a detectable amount" of LSD. Although petitioners pure LSD weighed only 50 milligrams, the court included the total weight of the paper and LSD, 5.7 grams, in calculating their sentences, thus requiring the imposition of the mandatory minimum sentence. The 5.7 grams was also used to determine the base offense level under the United States Sentencing Commission Guidelines Manual (Sentencing Guidelines). The Court of Appeals affirmed,