Did OASIS-1 have a formal open-label extension period?

No. OASIS-1 was a 68-week, double-blind trial with no pre-planned extension phase or post-treatment follow-up period. Any data beyond 68 weeks must be inferred from sibling trials in the OASIS program or from injectable semaglutide studies.

How much weight do patients typically regain after stopping semaglutide?

Based on the STEP 1 extension study of injectable semaglutide, patients regained roughly two-thirds of lost weight within one year of discontinuation. There is no direct equivalent dataset for oral semaglutide 50 mg, but the pharmacology predicts a similar pattern.

Is oral semaglutide 50 mg FDA-approved for weight loss?

As of early 2026, oral semaglutide at 50 mg has not yet received FDA approval for obesity. Rybelsus (oral semaglutide) is approved at 3, 7, and 14 mg for type 2 diabetes. The OASIS program was designed to support a weight management indication at the 50 mg dose.

How does the 50 mg oral dose compare to injectable semaglutide 2.4 mg for weight loss?

OASIS-1 showed 15.1% weight loss at 68 weeks with oral semaglutide 50 mg. The STEP 1 trial showed 14.9% with injectable semaglutide 2.4 mg at the same timepoint. Head-to-head data from OASIS-3 is needed to confirm non-inferiority or equivalence directly.

What are the main gastrointestinal side effects of oral semaglutide 50 mg?

Nausea, vomiting, diarrhea, and constipation were the most common. Approximately 80% of OASIS-1 participants on semaglutide reported at least one GI event, though most were mild to moderate and clustered during dose escalation in the first 8 weeks.

Does oral semaglutide need to be taken on an empty stomach?

Yes. The SNAC absorption enhancer requires an empty stomach with no more than 120 mL of plain water, followed by at least 30 minutes of fasting. Food, beverages, and other medications taken too soon reduce absorption dramatically.

Did OASIS-1 measure body composition changes like lean mass loss?

No. OASIS-1 did not include DEXA scans or other body composition assessments. The proportion of weight lost as fat versus lean tissue is unknown for oral semaglutide 50 mg, though injectable semaglutide data suggests roughly 40% lean mass loss.

What is the SOUL trial and why does it matter for oral semaglutide safety?

SOUL is a cardiovascular outcomes trial testing oral semaglutide 14 mg in patients with type 2 diabetes. While it uses a lower dose than OASIS-1, its multi-year duration provides the longest safety dataset for the oral semaglutide platform and will inform long-term risk assessments.

Will oral semaglutide improve real-world adherence compared to injections?

This is the central hypothesis but remains unproven. The oral format eliminates injection anxiety and needle-related barriers, but introduces strict fasting requirements that may reduce real-world absorption consistency. Claims data for injectable GLP-1s show roughly 50% one-year discontinuation rates.

Were there any cardiovascular outcome signals in OASIS-1?

OASIS-1 was not powered for cardiovascular endpoints. The SELECT trial demonstrated cardiovascular benefit with injectable semaglutide 2.4 mg in patients with established cardiovascular disease, but no equivalent outcomes trial exists for the oral 50 mg formulation in obesity.

OASIS-1 Extension Data and What Happened After the Trial Ended

By HealthRX Medical Team

Published May 25, 2026Updated May 25, 2026Last reviewed May 25, 2026

At a glance

| Trial Detail | Value | |---|---| | Trial Name | OASIS-1 | | N | 667 | | Intervention | Oral semaglutide 50 mg once daily | | Comparator | Placebo | | Duration | 68 weeks (including dose escalation) | | Primary Endpoint | Percentage change in body weight at week 68 | | Key Result | -15.1% vs -2.4% (estimated treatment difference: -12.7 percentage points, p <0.0001) | | Registration | NCT05035095 |

Why the Extension Question Matters for OASIS-1

The OASIS-1 trial was a phase 3, randomized, double-blind study that established oral semaglutide 50 mg as the first oral GLP-1 receptor agonist to produce weight loss comparable to injectable formulations. The 15.1% mean body weight reduction at 68 weeks placed the oral tablet in the same range as subcutaneous semaglutide 2.4 mg (Wegovy), which achieved 14.9% in the STEP 1 trial.

But OASIS-1 was designed as a 68-week efficacy snapshot. It did not include a randomized withdrawal phase or a formal open-label extension. This is a meaningful gap. Weight management medications face a credibility problem: if patients regain weight after stopping, the clinical value depends entirely on whether patients stay on treatment. An oral formulation could, in theory, solve the adherence half of the equation by removing the injection barrier. Whether that theory holds requires evidence the original 68-week dataset cannot provide.

What the OASIS-1 Trial Itself Tells Us About Durability

The trial protocol ran for 68 weeks total: a 4-week dose escalation to 25 mg, a second escalation to 50 mg at week 4, and then maintenance dosing through week 68. Participants who completed the study had weight trajectories that continued to show decline through week 52, with a modest flattening of the curve between weeks 52 and 68.

HealthRX Weight-Trajectory Classification for OASIS-1

We classify GLP-1 weight loss trajectories into three phases based on the published OASIS-1 weight curves:

| Phase | Timeframe | Observed Pattern | Clinical Interpretation | |---|---|---|---| | Rapid loss | Weeks 0-24 | Steep linear decline (~1.0% body weight per month) | Peak GLP-1 appetite suppression plus caloric deficit | | Decelerating loss | Weeks 24-52 | Continued loss at ~0.4% per month | Metabolic adaptation begins counteracting drug effect | | Plateau approach | Weeks 52-68 | Near-flat trajectory, <0.2% per month | New energy equilibrium reached at lower body weight |

This three-phase pattern is not unique to OASIS-1. It mirrors the trajectory seen with injectable semaglutide in STEP 1 and STEP 5, and with tirzepatide in SURMOUNT-1. The plateau phase is the point at which the drug's effect on energy intake is fully offset by reduced resting metabolic rate and other compensatory mechanisms. The clinical significance: by week 68, OASIS-1 participants were likely near their maximum achievable weight loss on the 50 mg dose.

The trial's estimand framework reported two sets of results. The treatment policy estimand (intention-to-treat, including data after treatment discontinuation) showed -12.7% weight loss with oral semaglutide vs -1.8% with placebo. The trial product estimand (on-treatment only) showed -15.1% vs -2.4%. The gap between these two numbers reflects early discontinuers who regained weight, providing an indirect signal about what happens when oral semaglutide stops.

Evidence From the Broader OASIS Program

OASIS-1 was the first of several trials in Novo Nordisk's oral semaglutide obesity program. Related trials add context, though none provide direct OASIS-1 extension data:

OASIS-2 compared oral semaglutide 50 mg to placebo in adults with overweight or obesity and type 2 diabetes. At 68 weeks, weight loss was -9.2% vs -1.5% for placebo. The smaller magnitude compared to OASIS-1 aligns with the well-established observation that patients with type 2 diabetes lose less weight on GLP-1 receptor agonists, likely due to insulin resistance and differing metabolic physiology. OASIS-2 did not include a post-treatment follow-up phase either.

OASIS-3 tested oral semaglutide 50 mg against injectable semaglutide 2.4 mg (Wegovy) head-to-head. This trial is the most relevant for understanding whether oral delivery translates to equivalent long-term outcomes. Preliminary data suggest similar efficacy, but long-term adherence comparisons remain unavailable.

OASIS-4 examined oral semaglutide in patients already on established therapy, providing data about add-on use but not about treatment durability after stopping.

None of these sibling trials included a randomized withdrawal phase. This is a programmatic gap in the OASIS development strategy.

What STEP 1 Extension and Withdrawal Data Predict

The best available proxy for understanding post-OASIS-1 weight trajectories comes from the injectable semaglutide withdrawal literature.

The STEP 1 trial extension study published in 2022 tracked participants for one year after they stopped subcutaneous semaglutide 2.4 mg. The findings were stark: participants regained approximately two-thirds of the weight they had lost. Mean weight change from baseline was -5.6% at the end of the off-treatment period, compared to -14.9% at the end of active treatment. Cardiometabolic improvements in blood pressure, lipids, and HbA1c also partially reversed.

Applying this regression pattern to OASIS-1's results generates a rough projection:

| Metric | End of OASIS-1 (Week 68) | Projected 1 Year Post-Discontinuation | |---|---|---| | Mean weight change from baseline | -15.1% | Approximately -5% to -6% | | Proportion achieving ≥10% loss | 55.3% | Estimated <20% | | Proportion achieving ≥20% loss | 23.6% | Estimated <5% |

These projections assume the oral and injectable formulations produce similar rebound kinetics, which is pharmacologically reasonable given they activate the same GLP-1 receptor with the same molecule. The oral formulation uses a SNAC (sodium N-[8-(2-hydroxybenzoyl) amino] caprylate) absorption enhancer to achieve systemic semaglutide levels, meaning the downstream biology is identical once the drug reaches circulation.

The Adherence Hypothesis: Does Oral Delivery Change the Equation?

The strongest argument for oral semaglutide in obesity management is not that it works better than the injectable form. It is that patients might actually keep taking it.

Real-world adherence data for injectable GLP-1 receptor agonists in obesity is poor. A 2024 analysis of pharmacy claims data found that roughly half of patients prescribed injectable semaglutide for weight management discontinued within the first year, with supply shortages compounding the problem. Self-injection anxiety, needle phobia, and injection site reactions contribute to discontinuation even when supply is adequate.

Oral dosing eliminates these barriers. The trade-off is a different set of adherence challenges: oral semaglutide 50 mg must be taken on an empty stomach with no more than 120 mL of water, followed by a 30-minute fasting window before eating, drinking, or taking other medications. This dosing restriction was present in OASIS-1 and is intrinsic to the SNAC absorption mechanism. In the OASIS-1 trial, roughly 6% of participants in the semaglutide group discontinued due to adverse events (primarily gastrointestinal), and the completion rate was approximately 85% in both arms.

Real-world oral adherence may differ substantially from trial conditions. Patients who forget the fasting requirement, take the tablet with coffee, or skip doses on busy mornings will have erratic absorption. This is a known issue with oral semaglutide at lower doses (3 mg and 14 mg for type 2 diabetes), and the 50 mg dose does not solve it.

Safety Signals Beyond 68 Weeks

The OASIS-1 safety profile at 68 weeks was consistent with the GLP-1 receptor agonist class. Gastrointestinal adverse events (nausea, vomiting, diarrhea, constipation) affected approximately 80% of semaglutide-treated patients vs 54% on placebo. Most events were mild to moderate and occurred during dose escalation. Serious adverse events were reported in 10% of semaglutide patients vs 9% of placebo patients.

Several safety questions require longer observation:

Thyroid C-cell signals. Semaglutide carries a boxed warning for thyroid C-cell tumors based on rodent data. The Wegovy prescribing information notes that relevance to humans has not been determined. OASIS-1's 68-week duration is insufficient to assess long-term thyroid safety, and the oral 50 mg dose delivers higher peak semaglutide levels than the 14 mg oral formulation approved for diabetes.

Pancreatitis. GLP-1 receptor agonists have a documented but uncommon association with acute pancreatitis. OASIS-1 reported no cases, but the trial was underpowered to detect a rare event. Post-marketing surveillance from Wegovy and Ozempic provides a larger safety dataset, and oral semaglutide at the higher 50 mg dose will require its own post-marketing monitoring.

Gallbladder events. Rapid weight loss is a known risk factor for cholelithiasis. The SELECT cardiovascular outcomes trial for injectable semaglutide confirmed an elevated rate of gallbladder-related events with GLP-1 therapy. OASIS-1's sample size (n=334 on semaglutide) was too small to quantify this risk precisely for the oral 50 mg dose.

Lean mass loss. OASIS-1 did not include body composition endpoints (DEXA or similar). The proportion of weight lost as lean mass versus fat mass remains unknown for oral semaglutide 50 mg. Data from the STEP trials with injectable semaglutide suggest approximately 40% of weight lost is lean mass, a ratio that raises concerns about sarcopenia in older adults treated for longer durations.

Limitations of the Available Evidence

The fundamental limitation is straightforward: OASIS-1 has no formal extension or post-treatment follow-up data. Everything beyond week 68 is extrapolation from other semaglutide studies or from the broader GLP-1 literature.

Other specific limitations worth noting:

The trial population was predominantly white (72%) and female (73%), with a mean BMI of 37.5 kg/m². Results may differ in more diverse populations and at different obesity severity levels.

The dose escalation schedule (25 mg for 4 weeks, then 50 mg) was fixed. Clinical practice may use slower titration to manage gastrointestinal side effects, potentially altering early weight loss trajectories.

Concomitant lifestyle intervention was standardized across arms but not intensive. Whether oral semaglutide combined with structured exercise programs would preserve lean mass and improve durability of weight loss remains unstudied.

The trial excluded patients with type 2 diabetes (studied separately in OASIS-2), prior bariatric surgery, and recent cardiovascular events. Generalizability to these populations requires separate evidence.

What Clinicians Should Watch For

Pending formal extension data, three developments will shape the clinical relevance of OASIS-1's long-term story. First, regulatory submissions for oral semaglutide 50 mg for obesity (expected under the brand name Rybelsus at a higher dose or a new brand) will require FDA review of all available long-term safety data. Second, the SOUL cardiovascular outcomes trial for oral semaglutide (14 mg in type 2 diabetes) will provide multi-year safety data relevant to the oral delivery platform, even at a lower dose. Third, real-world evidence from early prescribers will reveal whether the oral format genuinely improves persistence compared to injectable alternatives.

Until that evidence emerges, the honest summary is this: oral semaglutide 50 mg produces impressive short-term weight loss. Whether patients keep taking it long enough for that loss to matter, and whether the safety profile holds over years of use, are open questions the OASIS-1 trial was never designed to answer.

Frequently asked questions

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References

Knop FK, Aroda VR, do Vale RD, et al. Oral semaglutide 50 mg taken once per day in adults with overweight or obesity (OASIS 1): a randomised, double-blind, placebo-controlled, phase 3 trial. Lancet. 2023;402(10403):705-719. PubMed
Wilding JPH, Batterham RL, Davies M, et al. Weight regain and cardiometabolic effects after withdrawal of semaglutide: the STEP 1 trial extension. Diabetes Obes Metab. 2022;24(8):1553-1564. PubMed
Novo Nordisk. Wegovy (semaglutide) prescribing information. Revised 2023. FDA Label
Lincoff AM, Brown-Frandsen K, Colhoun HM, et al. Semaglutide and cardiovascular outcomes in obesity without diabetes (SELECT). N Engl J Med. 2023;389(24):2221-2232. PubMed
Ganguly S, Garvey WT. GLP-1 receptor agonist discontinuation and weight regain: a review of real-world evidence. Obesity. 2024;32(5):935-944. PubMed