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designer drug de·sign·er drug (dĭ-zī'nər)
A drug with properties and effects similar to a known hallucinogen or narcotic but having a slightly altered chemical structure, especially such a drug created in order to evade restrictions against illegal substances.
A synthesized narcotic, often of much higher potency than those produced from plants: These new ''designer drugs'' or ''super narcotics'' are triply dangerous/ Out here urine testing has spawned the ''designer'' drug game (1980s+)