Two years later, he commented in an editorial for "PLOS Medicine" that activist groups have derailed several pre-exposure prophylaxis (PREP) clinical trials. He also expressed frustration that activist groups have prevented newer CCR5 receptor antagonists from being tested in Europe. However, Lange was criticised for neglecting the needs of sex workers in the trials, and other researchers asserted that the concerns raised by activists are "entirely legitimate" since the known toxic effects of so-called 'pre-exposure' drugs will lead to liver failure and kidney disease, thereby killing people rather than protecting them.