In the past years, there has been a mounting trend toward the addition of sympathomimetic stimulants in sports and weight loss supplements sold in the US and claimed to be from natural constituents. The latest among those pharmaceutical stimulants is 1,5-dimethylhexylamine (1,5-DMHA or octodrine), an ingredient in newly introduced sports and weight loss supplements with its ‘natural’ origin being cited from Aconitum or Kigelia plants. In order to validate the natural existence of 1,5-DMHA, two GC/MS methods were developed. One method involved using thick film megabore capillary columns to analyze the underivatized 1,5-DMHA. The second method was to determine enantiomeric distribution of 1,5-DMHA. Fifteen Aconitum or Kigelia plant samples originating from various locations were analyzed, and none of them contained 1,5-DMHA within the limit of detection (25 ng/mL) of the method. In contrast, although 1,5-DMHA was listed on the labels or website for all the 13 dietary supplements, only four products were found to contain this compound, with the highest quantity being reported as 112 mg per serving size. This is equivalent to more than three times the highest pharmaceutical dose established in Europe. The enantiomeric ratios of 1,5-DMHA in these products were determined to be between 0.9–1.0 (expressed as peak area ratio of one enantiomer over another), suggesting racemic nature. Interestingly, two byproducts from 1,5-DMHA synthesis were identified in commercial supplements containing 1,5-DMHA, indicating that 1,5-DMHA indeed originated from a poor quality source. Overall, the significant amount of 1,5-DMHA observed in the supplements, the enantiomeric distribution and the presence of the synthetic byproducts all suggested the synthetic origin of 1,5-DMHA in the commercial products.