The extract of P. amygdalus var. amara is known for its health benefits, which include lowering diabetes and heart disease risks. In eight human tumor cell lines, P. amygdalus var. amara demonstrated potent anti-cancer activity, including NB4, Huh-7, A-549, SKOV-3, PC-3, T-24, U937, and Hep-2. There was a notable change in the morphology of nearly all cancer cell lines, and cancer cells continued to exist. Incubation for 12 h, 24 h, 48 h, or 72 h resulted in the lowest viable cell concentration at 48 h, which was 34.65% lower than that of the non-treated cells. During exposure to the extract, the majority of cells lost their typical morphology and shrank in size. According to the cell viability data, the P. amygdalus var. amara treatment significantly decreased the cancer cells’ growth in most cancer cell lines when doses and time were taken into consideration.