Abstract: Purpose of research: Describe prescribing patterns in Australian Vietnam veterans, identify CYP2C19-metabolised medications using established pharmacogenetic (PGx) resources, characterise CYP2C19 profiles of veterans and assess the potential clinical impact of these medications. Major findings: Among 283 veterans with CYP2C19 profiles, 256 reported current medications use, with a mean prescribed medication of 5.4. Of these, 89 veterans (34.7%) were prescribed at least one medication with CYP2C19 PGx recommendation. Notably, 52 veterans (58.4%) had CYP2C19 profiles that may be at risk of therapeutic failure or adverse effects. Prescribed medications also included six CYP2C19 inhibitors and one inducer, with potential to induce phenoconversion and impact drug metabolism. Conclusion: Veterans experienced high levels of polypharmacy and frequently carried CYP2C19 phenotypes associated with increased risk of therapeutic failure or adverse effects. The presence of CYP2C19 inhibitors and inducers raises the potential for phenoconversion, where CYP2C19 profiles may be placed at risk. Given their similarities to the broader older population, these findings suggest that both groups may benefit from pre-emptive PGx testing. Furthermore, ongoing monitoring of drug-gene and drug-drug interactions remains essential to optimise medication safety and efficacy in these high-risk individuals.