Excerpts from the peer reviewed study abstract The Anticancer Potential of Psidium guajava (Guava) Extracts as published of the National Institutes of Health website. The full abstract is linked above.

“The fruits, leaves, and bark of the guava (Psidium guajava) tree have traditionally been used to treat a myriad of ailments, especially in the tropical and subtropical regions. The various parts of the plant have been shown to exhibit medicinal properties, such as antimicrobial, antioxidant, anti-inflammatory, and antidiabetic activities. Recent studies have shown that the bioactive phytochemicals of several parts of the P. guajava plant exhibit anticancer activity. This review aims to present a concise summary of the in vitro and in vivo studies investigating the anticancer activity of the plant against various human cancer cell lines and animal models, including the identified phytochemicals that contributes to their activity via the different mechanisms. In vitro growth and cell viability studies, such as the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay, the sulforhodamine B (SRB) assay, and the trypan blue exclusion test, were conducted using P. guajava extracts and their biomolecules to assess their effects on human cancer cell lines. Numerous studies have showcased that the P. guajava plant and its bioactive molecules, especially those extracted from its leaves, selectively suppress the growth of human cancer cells without cytotoxicity against the normal cells. This review presents the potential of the extracts of P. guajava and the bioactive molecules derived from it, to be utilized as a feasible alternative or adjuvant treatment for human cancers. The availability of the plant also contributes towards its viability as a cancer treatment in developing countries.”

“The guava leaf extract was shown to inhibit the PGHS-1 and -2 production in the cancer cells, inhibit the PGHS synthesis, and suppress their cyclooxygenase reaction and DNA synthesis rate [9]. Another study was conducted using the HCT116 colon cancer, Caco-2 epithelial colorectal adenocarcinoma, SW620 lymph node-metastasis colon adenocarcinoma cell lines, and COLO320DM cells to evaluate the anticancer potential of essential oil of P. guajava leaf extract from Ecuador. The cell viability of the cancer cells after treatment with the extract was determined using the trypan blue exclusion test. The IC50 value of the extract was found to be around 50 μg/mL when tested on the HCT116 cells. At 50 μg/mL, the growth of all three cell lines was reduced by 50-60% after incubation with the extract for 24-48 h. As the extract did not affect the growth of peripheral blood mononuclear cells (PBMCs), it was concluded that the extract’s inhibition of cancer cell growth is due to its antiproliferative rather than the cytotoxic effect [26].”