Here’s what we do know: Tenofovir, which hit the market in 2001, is one of the most prescribed HIV meds in the world. Its original form—tenofovir disoproxil fumarate (TDF), sold as the brand name Viread—is a component of many HIV regimens, including the tablet Truvada, which is also used as PrEP, a daily prevention pill. TDF can be toxic to kidneys and bones. More than a decade ago, tenofovir manufacturer Gilead Sciences developed a less harmful version called tenofovir alafenamide (TAF) but shelved the research for years. Last November, the FDA approved Genvoya, a combo pill that includes TAF. (The newer tenofovir isn’t approved for PrEP.)

Here’s what a lawsuit by the AIDS Healthcare Foundation alleges: Gilead could have developed the safer version of tenofovir earlier but didn’t because it wanted to boost profits and extend its patents. Not only did Gilead block competition, the lawsuit claims, but it also forced people with HIV to take the med with higher bone and kidney toxicities.

Gilead counters that it had stopped research on the new tenofovir because at the time it was focused on developing a new type of HIV drug called an integrase inhibitor.