This paper was intended to efficiently extract multiclass prohibited substances in human sport drug testing by using supramolecular solvents (SUPRASs) made up of cubosomes. These SUPRASs, here first reported, are synthesized by the salt-induced coacervation of 1,2-hexanediol in urine. The formation of square and rounded cubosomes with a size range of 140-240 nm was confirmed by electron microscopy. These nanostructures consisted of 1,2-hexanediol, salt, and a high water content (36-61%, w/w). Their applicability in multiclass determinations was investigated by the extraction of 92 prohibited substances (log P from 2.4 to 9.2) belonging to the 10 categories of the World Anti-Doping Agency's (WADA) list. Variables influencing both recoveries and matrix effects were optimized. Cubosomic SUPRASs showed high extraction efficiency and interference removal capability, which was attributed to their large hydrophilicity and surface area. Both features were superior to those of the other 11 SUPRASs that were based on sponge droplets and inverted hexagonal aggregates and to those of conventional organic solvents. A sport drug-testing method based on cubosomic SUPRAS-LC-ESI-MS/MS was proposed and validated. Around 82-95% of drugs were efficiently extracted (recoveries 70-120%) in urine samples, and 81-92% did not present matrix effects. The method detection limits (0.001-4.2 ng mL-1) were all far below WADA's limits. The proposed SUPRAS-based sample treatment is as simple as QuEChERS, but the distinctive features of cubosomes confer them high capability in multiclass determinations.