Tanacetum parthenium, commonly known as feverfew, is a perennial medicinal herb renowned for its therapeutic properties, particularly attributed to the sesquiterpene lactone parthenolide. This study explores the regulatory impact of Trichostatin A (TSA), an epigenetic modulator, on the expression of genes associated with parthenolide biosynthesis and accumulation in T. parthenium. We assessed the expression profiles of key genes, namely Germacrene A synthase (GAS), Parthenolide synthase (PTS), and Hydroxy-2-methyl-2-(E)-butenyl 4-diphosphate reductase (HDR) with qRT-PCR. The experimental approach involved treating feverfew plants with varying concentrations of TSA through seed pretreatment under in vitro conditions and foliar spray on in vivo-cultured plants. Our findings indicate that specific concentrations of TSA, notably 0.5 µM and 1 µM, positively modulate the expression of GAS and PTS genes, thereby influencing the final concentration of parthenolide. This research provides valuable insights into the potential of TSA as a strategic tool for enhancing secondary metabolite production in medicinal plants.