According to the US based drugs.com,[1] the use of papaya materials for medicinal purposes is (with some exceptions) not supported by conventional scientific data.[2]

But, as to be expected, there are people who would swear by the medicinal value of the papaya leaf latex (‘juice’).[3]  

Their claims now have the support of a recent animal (rats) study.[4] This is by a team from the Malaysian Herbal Medicine Research Center[5] which concluded that (a) the extract can increase platelet levels of dengue fever patients and (b) the extracts were not toxic.[6]

The following off-the-cuff comments may be tentatively made about this finding that the papaya latex is not toxic:
  • It appears that the team would regard the papaya latex as ‘toxic’ only if it causes death or serious harm such as serious damage to important body organs. That’s selectively using a rather limited definition of the word ‘toxic’.[7]
  • Although the papaya latex did not kill the rats, the Malaysian researchers found there were some changes inside the rats’ bodies.[8] These could be signs that the rats were adversely affected by the papaya latex fed to them. It is not unlikely that their organs signalled the likelihood that although the canary in the coalmine is still alive, it may have got sick from something toxic in its feed.[9]
  • The research finding may possibly encourage moreMalaysians to drink the latex as an antidote againstdengue fever. It is noted that the Star online reported a young man with dengue fever ‘plucked papaya leaves, ground them up, and drank the bitter dark green juice.’[10]  
  • There is another side to the good story about the wonders of papaya. People with dengue fever may find it useful to be aware of this side of the story before swallowing the bitter ‘juice’ of papaya leaves. It may also be of use to others wanting to use papaya latex supplements for various illnesses. The following are four points to note:

1.  The ‘shining star of papaya nutrition’ is papain.[11] The following are some things to know about papain:
  • It is an enzyme in papaya that helps digest protein and reduces inflammation.[12] It is in the latex of unripe papaya.[13]
  • Papaya leaves are considered the most powerful element of the plant as they have high levels of papain and 15 times the digestible protein of fully ripened fruit.[14]
  • Papain can be toxic. The following suggests that there are serious enough concerns for the US Food and Drugs Administration to issue a public warning.[15] On September 23, 2008, it warned companies to stop marketing a solution containing papain for use in irrigating tissues of the eyes (ophthalmic balanced salt solutions)and also the marketing of topical drug ointments[16]containing papain. The ointments containing papain had then been marketed for use to deal with various ulcers (diabetic ulcers, pressure ulcers, varicose ulcers), and infected wounds.[17] Why this prohibition? According to Janet Woodcock, M.D., director for the FDA’s Center for Drug Evaluation and Research, "These products have put consumers' health in jeopardy”. There had been reports ofpermanent vision loss with such salt solutions.[18] There had also been reports of a serious drop in blood pressureand increased heart rate from the topical papain products.[19]  
     
2.  Papaya latex can be a severe irritant and vesicant on skin.[20] The US FDA also indicated people with latex sensitivity may be at increased risk of suffering an adverse reaction to a topical papaindrug product.[21] 

3. A website of the Center for New Crops & Plant Products,Department of Horticulture at Purdue University (USA) has the following statements about the toxicity of papaya latex:[22]“Externally the latex is irritant, dermatogenic, and vescicant.[23]Internally it causes severe gastritis. [24] Some people are allergic to the pollen, the fruit, and the latex. Papain can induce asthma and rhinitis. The acrid fresh latex can cause severe conjunctivitis[25] and vesication.[26] According to Morton (1977)[27] the latex will digest tissue and cause sores under rings and bracelets, while it has been used internally for malicious poisoning”.[28]

4. Like avocados and bananas, papayas contain substances called chitinases that are associated with the latex-fruit allergy syndrome.[29] There is strong evidence of the cross-reaction between latex and these foods.[30]