Maca (L. meyenii) for improving sexual function: A systematic review 

A 2010 systematic review has been performed on the effects of maca on sexual function in humans. Four randomized clinical trials (RCT) met all the inclusion criteria. According to the review, two RCTs suggested a significant positive effect of maca on sexual dysfunction or sexual desire in healthy menopausal women or healthy adult men, while the other RCT failed to show any effects in healthy cyclists.  

References:

Shin BC, Lee MS, Yang EJ, Lim HS, Ernst E. Maca (L. meyenii) for improving sexual function: a systematic review. BMC Complement Altern Med. 2010;10:44. Published 2010 Aug 6. doi:10.1186/1472-6882-10-44 https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2928177/