The study found that the average MTQ concentration in all four batches of tablets used in the study differed significantly, making it impossible to determine that, on the basis of MTQ concentration alone, the batches with a similar logo originated from the same manufacturer or manufacturing batch. The four batches either originated from different clandestine laboratories or manufacturing batches. The large within-batch coefficients of variation found in the MTQ concentration of the sample groups can typically be due to poor homogenization procedures in clandestine laboratories. This circumstance poses a toxicity risk, since drug abusers might overdose due to an underestimation of the dosage ingested. The description of the methodology used addresses the reagents and chemicals used, the equipment used, the sample preparation and extraction procedures, the GC-MS detection procedure, standards and calibration curves, the sampling procedure, assay validation, and statistical analysis. 1 table, 7 figures, and 14 references