Papaya tree is commonly found in tropical areas around the world. The fruits are consumed as food and medicine; dried and powdered stems and leaves are used to prepare medicinal teas against infections and to improve digestion. Papaya leaves and their extracts are also marketed as dietary supplements to enhance the immune system, improve platelet function, and prevent chemotherapy-related adverse effects.

Papaya leaves exhibit immunomodulatory ⁽¹⁾, antioxidant ⁽⁹⁾, and anticancer ^(11) (12) effects in vitro. The leaf extracts contain antibacterial compounds that inhibit the growth of a wide variety of Gram-positive and Gram-negative bacteria ⁽⁴⁾. In mice, a powdered suspension of papaya leaves increased thrombocyte count ⁽²⁾ and a water extract reduced alcohol-induced stomach damage ⁽⁵⁾. Hypoglycemic effects were also reported with use of papaya leaf extract in streptozotocin-induced diabetic rats ⁽¹⁰⁾, and it was shown to have low toxicity ⁽⁶⁾.

According to a case report, a water extract of papaya leaves increased the platelet count of a patient with Dengue fever ⁽³⁾. Data from a randomized study confirm these findings in patients with thrombocytopenia associated with Dengue fever ⁽¹³⁾. An international patent has been filed for its use in increasing low platelet counts ⁽⁷⁾. Papaya leaf extracts should not be used as a treatment for cancer or for low platelet count until more is known about its efficacy and adverse effects in humans.