Here's a question that sounds simple but isn't: why do people with HIV have to take a pill every single day? The answer, historically, has been that the drugs don't last long enough in the body to work on a weekly schedule. But Gilead Sciences (GILD) and Merck (MRK) just released data that suggests that might be changing.
On Tuesday, the two drugmakers reported detailed Phase 3 results for their investigational once-weekly oral HIV regimen, a combination of islatravir and lenacapavir (ISL/LEN). The data, which will be presented at the International AIDS Conference (AIDS 2026), showed that the weekly pill maintained viral suppression through 48 weeks in adults who switched from daily antiretroviral therapy. That's a big deal, because if approved, this could become the first once-weekly oral HIV regimen on the market.
The primary endpoint in both Phase 3 studies was non-inferiority—basically, proving that the weekly pill works as well as the daily standard of care. And it did. In the ISLEND-1 trial, zero participants on once-weekly ISL/LEN had HIV-1 RNA levels reaching 50 copies/mL or higher at Week 48. For context, HIV-1 RNA levels (viral load) measure the amount of virus in the blood, and keeping that number low is the whole point of treatment. In the daily Biktarvy group, 0.3% of participants had detectable virus. So the weekly pill actually looked a little better, though the difference wasn't statistically significant.
Side effects were similar between the groups. Treatment-related adverse events occurred in 13.5% of ISL/LEN participants and 13.2% of Biktarvy participants, with nausea and headache being the most common. Discontinuations due to side effects were low—2% for the weekly pill and 1.7% for daily Biktarvy. That's encouraging, because a new regimen isn't useful if people can't tolerate it.
The second trial, ISLEND-2, told a similar story. It was an open-label study where participants either got weekly ISL/LEN or stayed on their daily standard care. At 48 weeks, 0.3% of the weekly group had detectable virus versus 1.3% of the daily group. Again, non-inferiority was met. Treatment-related side effects were higher in the weekly group (18% vs. under 1%), but discontinuations remained low. The most common side effects were headache, nausea, and diarrhea.
Beyond just viral suppression, the studies also looked at patient satisfaction. Unsurprisingly, people preferred taking a pill once a week instead of every day. Participants who switched to the weekly regimen reported lower treatment burden and higher overall satisfaction. That might sound obvious, but in the real world, it matters. If patients are happier with their treatment, they're more likely to stick with it, which means better long-term outcomes.
Both Gilead and Merck are now planning to submit regulatory filings based on this data. If approved, the weekly pill could fundamentally change the standard of care for HIV. Instead of a daily reminder of the disease, patients might only think about it once a week. That's a meaningful improvement in quality of life.
As for the market's reaction? Merck shares were up 0.87% at $125.48, while Gilead shares were down 2.62% at $129.72 at the time of publication. The slight dip for Gilead might reflect the fact that a successful weekly pill could cannibalize sales of its daily HIV drugs like Biktarvy. But for patients, that's a trade-off worth making.
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