An Indian effort to pioneer a non-surgical, reversible vasectomy has run into an unexpected hurdle, as researchers are having difficulty finding volunteers for clinical trials of the new treatment, the Times of India reports.

The treatment, called RISUG (Reversible Inhibition of Sperm UnderGuidance), has already shown great promise in earlier phases of testing, as detailed earlier this year in GlobalPost.

According to the TOI, however, the phase-III trials which started in four centres in 2009 has only managed to recruit around 60 male volunteers against a target of 200 (around 50 volunteers per center). In response, the Indian Council for Medical Research has asked regulators for permission to extend the trials to four more centers.