In an article published on the website of the world's foremost scientific journal, Nature, possible side effects of tongkat ali (Eurycoma longifolia) were listed as "a light headache, a slight fever or even a rash" for a few days.
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By Serge Kreutz (2010)
Referred-to results were "increased sexual desire, enhanced performance and general well-being".
As usually is the case with scientific articles, a payment is required to read the full article. However, an abstract can be read for free on the Nature website here:
http://www.nature.com/nm/journal/v11/n9/full/ nm0905-912a.html
Index of articles, click here.
Copyright Serge Kreutz