Why GSK’s Experimental HIV Drug Could Be a Safer Bet—And a Headache for Gilead by Sy Mukherjee @FortuneMagazine December 20, 2016, 8:58 PM EST E-mail Tweet Facebook Linkedin Share icons An experimental therapy from GlaxoSmithKline gsk could be just as effective as existing therapies for HIV/AIDS patients without the corresponding risk of toxic side effects, raising the possibility of a challenge to incumbent companies in the space like Gilead gild . In August, GSK announced that it was working on a major advance in HIV therapeutics that lopped off one-third of the drugs commonly used to treat the condition, which has gone from a death sentence to a manageable chronic disease over the last few decades thanks to medical advancements. Click here to subscribe to Brainstorm Health Daily, our brand new newsletter about health innovations. It appears that GSK’s efforts are beginning to bear fruit. The British drugmaker announced on Tuesday that a combination therapy of its dolutegravir (sold under the branded name Tivicay) and the Johnson & Johnson jnj medication rilpivirine proved just as effective for treating HIV patients as more conventional three- and even four-drug cocktails, according to Reuters. So why is this new advance a possible game-changer? The reason is two-fold: 1) HIV patients must continue taking their medications over the course of their lives to prevent a resurgence of the virus. 2) Nesting multiple drugs in a combination tablet can lead to side effects and become less tolerable the more they’re used over time. And that’s where the prospect of a two-drug regimen could strike fear into the hearts of leaders like Gilead, which has relied heavily on its HIV drug income to lift its finances. “The key debate remains whether Gilead will gain the upper hand again or whether a disruptive two-drug regimen becomes standard of care, favoring GSK,” UBS analyst Michael Leuchten told Reuters in an interview. GSK also recently launched a landmark HIV vaccine trial in South Africa.