Studies on the pyrolysis of the synthetic cannabinoid agonist UR-144 ((1-pentyl-1H-indol-3-yl)(2,2,3,3-tetramethylcyclopropyl)methanone) have shown that its major pyrolysis product is a tetramethylcyclopropane ring-opened alkene. Considering that smoking is a common way of ingesting synthetic cannabimimetics, the presence of the metabolites of this pyrolysis product would be expected in biological fluids. Using GC-MS and LC-MS-MS methods, a series of phase I metabolites of UR-144 and its pyrolysis product were detected in the urine samples from patients admitted to hospital with suspected drug intoxication. The metabolites were tentatively identified as the products of mono-hydroxylation, di-hydroxylation, mono-hydroxylation with formation of the carbonyl group on the N-alkyl chain, carboxylation and N-dealkylation with mono-hydroxylation. In the case of the UR-144 pyrolysis product, metabolites with hydration of the aliphatic double bond were also identified. The parent compounds were detected as trace amounts in some urine samples, and the hydrated derivative of the UR-144 pyrolysis product was detected in the majority of samples. The detection of mono-hydroxylated metabolites of UR-144 (LC-MS-MS) and mono-hydroxylated/with hydration metabolites of the UR-144 pyrolysis product (GC-MS) was found to be the most useful method of establishing UR-144 ingestion.