Manufacture and recreational use of methamphetamine can result in widespread chemical contamination throughout a property. Hydrogen peroxide (H₂O₂)-based cleaning products have shown success against a number of chemical contaminants including agents of chemical warfare, and biological contaminants such as anthrax. They are considered to be environmentally friendly and economically viable and, as such, are used by many companies within the methamphetamine decontamination industry. The oxidative decontamination of methamphetamine and ephedrine hydrochloride was investigated in this current study, employing a commercially available H₂O₂-based decontamination product, Bio-Oxygen® Chem Decon. Methamphetamine and ephedrine were observed to degrade following pseudo-first order kinetics of (1.9 ± 0.4) × 10⁻² min⁻¹ and (2.2 ± 0.3) × 10⁻² min⁻¹, respectively. Major oxidation products identified through GC-MS analyses were phenylacetone oxime (from methamphetamine) and benzaldehyde (from ephedrine). LC-MS analysis revealed the presence of a number of N-oxygenated intermediates which allowed for the elucidation of an N-oxidation decomposition pathway reminiscent of flavin-containing monooxygenase enzymes. Using this information, further targeted research can be performed to understand the behaviour and persistence of these reaction products and accurate assessments can be achieved to estimate their impact on the exposure risks associated with chemical decontamination of amphetamine-type stimulants (ATS).