The lithium-ammonia reduction method is one of the most common means of illicit methamphetamine manufacture in the United States. In this process, lithium serves as an electron source with ammonia as a solvent that allows the electrons to reduce the hydroxyl group of ephedrine to form methamphetamine. Since these conditions are similar to a classical Birch reduction in which sodium, ammonia, and an alcohol are used to reduce aromatic rings to form cyclohexadienes, the term Birch reduction has been used to describe this method. This cyclohexadine byproduct is not found in samples of methamphetamine produced from other manufacturing methods. In the current study, a sample enriched in this byproduct was produced and characterized by using nuclear magnetic resonance (NMR) spectroscopy, gas chromatography-mass spectrometry, infrared spectrophotometry, and ultraviolet spectrophotometry. The chemical structure of this byproduct was determined to be 1-(1',4'-cyclohexadienyl)-2-methylaminopropane (CMP). The sample of approximately 85 percent CMP was used to collect structural data. This data allowed the structure of the major component to be determined from first principles. Although these experiments do not provide direct information about the absolute stereochemistry at the 2 position, they do show that a single stereoisomer is formed. Based on proposed reaction mechanisms, it is more likely that the stereochemistry at this position is preserved from the starting material than that these conditions result in a total inversion of the stereochemistry at this center. 9 figures and 23 references