Viking Therapeutics Shows Patients Keep Up to 97% of Weight Loss on Monthly Dosing, With Tolerability Matching Placebo
Special call held September 22, 2026 on top-line results from VK2735 maintenance dosing study
Viking Therapeutics used a special conference call on September 22 to unveil top-line data from a novel Phase II maintenance-dosing study of VK2735, its dual GLP-1/GIP agonist for obesity, and the results answer one of the biggest open questions in the obesity drug category: can patients step down from weekly injections without losing the weight back. The data suggest they can, and the tolerability profile that came with it surprised even the company's own management team.
Weight loss holds even as dosing frequency drops by 85%
The 180-patient study put subjects through 21 weeks of weekly induction dosing, then transitioned them to either every-other-week dosing, monthly dosing, or placebo for an additional 12 weeks. Among patients who moved to every-other-week dosing, mean weight loss retention at week 33 ranged from 83% to 97% versus 61% for those switched to placebo. Patients transitioned to monthly dosing retained 82% to 90% of their weight loss, also comfortably ahead of the 61% placebo retention rate, with p-values below 0.01 across every cohort. CEO Brian Lian called the results "particularly impressive" given that "dosing was effectively reduced by up to 85% in these treatment groups." Notably, weight-loss maintenance appeared to trough in the initial weeks after the dosing transition before climbing back up through week 33, a pattern that caught the company off guard. "That was a bit of a surprise to us," Lian told analysts, "but it's very consistent and it clearly looks real."
17.5 mg weekly cohort posts 22% weight loss with no plateau in sight
Separately, patients maintained on the 17.5 mg weekly dose for the full 33 weeks lost 21.7% of body weight, or 22% placebo-adjusted, with the weight-loss curve still trending down at the end of the observation window. Management was careful to flag the limits of cross-trial comparisons, but noted that the currently approved GLP-1/GIP agonist has shown roughly 14% placebo-adjusted weight loss at 33 weeks, while the most advanced glucagon-triple agonist in development has posted approximately 17% at the same time point. Dr. Louis Aronne, former president of the Obesity Society and a longtime GLP-1 investigator who joined the call, was direct about where VK2735 now sits: "Based on my 35 years of experience doing this, I think it's pretty clear that VK2735 is highly effective. It's among the best that we've seen for available drugs at 22% weight loss over 33 weeks."
The real surprise: no resensitization to GI side effects
Perhaps the most consequential finding for investors is what happened to tolerability once dosing intervals stretched to four weeks. Rates of nausea, vomiting, diarrhea and constipation under both the every-other-week and monthly regimens were not meaningfully different from placebo, even though patients had been titrated roughly twice as fast as in the earlier Phase II VENTURE study. Lian said the company went into the trial only "cautiously optimistic" that tolerability would hold up under stretched dosing intervals, and the results exceeded that bar: "These data suggest that despite a gap of 4 weeks between doses, these individuals did not resensitize to GI adverse events such as nausea or vomiting." Aronne framed the clinical implication bluntly, arguing that persistence, not peak efficacy, is now the binding constraint on the category: "One of the things that we're learning is that maximum efficacy is maybe not the most important thing these days now that we've gotten such good efficacy, but that treatment persistence is actually key." He added that patients paying out of pocket already stretch their dosing intervals informally to save money, and that a label supporting less-frequent dosing "will be very appealing to patients knowing that they can take it less than every single week... but also the payers."
Clean safety data opens the door to testing higher doses
Because tolerability held up so well even under accelerated titration and extended dosing gaps, management indicated it now has room to explore higher maintenance doses than originally planned, a decision it has not yet finalized. Lian confirmed the study "opens the possibility to explore higher doses" given "no real impact on tolerability at all in the maintenance phase." The company is still finalizing which doses it will carry into the VANQUISH open-label extension studies, expected to begin in late 2026 or early 2027, and is awaiting FDA feedback on dose selection and frequency before locking that in. Analysts pressed on whether Viking might allow physician or patient choice between every-other-week and monthly regimens in that extension; Lian said the company is leaning toward incorporating both options.
Read-through to the oral franchise and Phase III
Viking is also advancing an oral tablet formulation of VK2735 and plans to start two Phase III oral studies mirroring the subcutaneous VANQUISH trials, with an oral maintenance study using the same 21-week induction, 12-week maintenance design set to begin imminently at doses of 17.5 mg, 27.5 mg and 55 mg. Because the oral program can lean on the subcutaneous safety database, Lian said those trials "will be significantly smaller than the subcu studies, still large studies, but quite a bit smaller and quite a bit less expensive as well." Management said it expects rapid enrollment given the "high level of enthusiasm" seen in the ongoing subcutaneous VANQUISH-1 and VANQUISH-2 trials, both of which are fully enrolled with results expected in 2027.
Caveats: small cohorts and unresolved head-to-head questions
Management and Aronne were both careful to caveat the read relative to the broader competitive set. Aronne pushed back on direct comparisons to Phase III data from tirzepatide or Pfizer's oral candidate, noting cohort sizes here were as small as a dozen patients per arm versus hundreds or thousands in registrational trials, and that "as the trials get larger, the weight loss is not necessarily as great as it has been." He also flagged an unresolved biological question around the rapid weight-loss velocity: "some people have suggested that if you go past a certain velocity of weight loss, you could wind up losing more lean mass," a variable Viking has not yet measured and will need to address in future trials. Several dose-response readings in the data, including a slight downtick in efficacy at the highest 22.5 mg induction dose and an outlier 15% diarrhea rate in one every-other-week cohort, were attributed by management to small sample sizes rather than genuine signal.