STEP-5 Trial: A Plain-English Overview of What It Established

At a glance

| Detail | Value | |---|---| | Trial name | STEP-5 (Semaglutide Treatment Effect in People with Obesity, Study 5) | | N | 304 randomized (2:1 semaglutide : placebo) | | Intervention | Semaglutide 2.4 mg subcutaneous injection, once weekly | | Comparator | Matched placebo injection, once weekly | | Duration | 104 weeks (2 years) | | Primary endpoint | Percentage change in body weight from baseline to week 104 | | Key result | −15.2% semaglutide vs −2.6% placebo (estimated treatment difference: −12.6 percentage points; p < 0.0001) | | Registration | NCT03693430 |

The question STEP-5 set out to answer

By mid-2020, four large trials in the STEP program had already demonstrated that semaglutide 2.4 mg produced meaningful weight loss over 68 weeks (roughly 16 months). Clinicians, however, wanted to know something different: does the weight stay off if patients keep taking the drug for a second year? Or does the body adapt and the benefit erode?

STEP-5 was designed specifically to answer that durability question. It ran for 104 weeks, making it the longest controlled evaluation of semaglutide 2.4 mg for weight management published at the time. The trial was double-blind and placebo-controlled, with every participant also receiving lifestyle counseling (a 500 kcal/day deficit and 150 minutes of weekly physical activity). This design meant any weight difference between groups could be attributed to the drug itself, not just behavior change.

Who was enrolled

Investigators recruited adults aged 18 or older with a BMI of 30 kg/m² or higher, or a BMI of 27 kg/m² or higher with at least one weight-related comorbidity such as hypertension, dyslipidemia, obstructive sleep apnea, or cardiovascular disease. People with diabetes were excluded (the separate STEP-2 trial covered that population).

Of the 304 participants randomized, 304 were included in the intention-to-treat analysis. The average baseline characteristics were:

| Characteristic | Semaglutide group (n = 199) | Placebo group (n = 101) | |---|---|---| | Mean age | 47 years | 48 years | | Female | 78% | 75% | | Mean body weight | 106 kg | 105 kg | | Mean BMI | 38.5 kg/m² | 38.3 kg/m² |

The population skewed heavily female (about 77% across both arms), which is common in obesity trials but worth noting when applying results to male patients. Most participants were white, limiting the generalizability to other racial and ethnic groups.

What participants received

Semaglutide was escalated slowly to reduce gastrointestinal side effects. Participants started at 0.25 mg weekly and increased the dose every four weeks until reaching the target of 2.4 mg at week 16. The same escalation schedule was followed in the placebo arm with matched injections. Both groups received monthly lifestyle counseling throughout the trial, reinforcing dietary and exercise targets.

This 16-week dose escalation mirrors the protocol in the FDA-approved prescribing information for Wegovy (the brand name for semaglutide 2.4 mg in obesity), which means the trial closely reflects real-world dosing.

Primary and secondary endpoints

The co-primary endpoints were:

1. Percentage change in body weight from baseline to week 104
2. Proportion of participants achieving ≥5% weight loss at week 104

Key secondary endpoints included the proportion achieving ≥10%, ≥15%, and ≥20% weight loss, changes in waist circumference, systolic blood pressure, and lipid parameters.

What the trial found

Weight loss results

The headline numbers at 104 weeks:

| Outcome | Semaglutide 2.4 mg | Placebo | Difference | |---|---|---|---| | Mean weight change | −15.2% | −2.6% | −12.6 pp (p < 0.0001) | | ≥5% weight loss | 77.1% | 34.4% |, | | ≥10% weight loss | 61.8% | 13.3% |, | | ≥15% weight loss | 52.1% | 7.0% |, | | ≥20% weight loss | 36.1% | 3.0% |, |

More than one in three patients on semaglutide lost at least 20% of their starting weight over two years. In the placebo group, that figure was 3%.

The weight trajectory matters

A critical detail buried in the time-course data: weight loss in the semaglutide group did not plateau at 68 weeks and rebound. Instead, the weight curve flattened around week 60 and held steady through week 104. This plateau pattern suggests the drug reaches a pharmacological equilibrium rather than losing effectiveness. Patients maintained the vast majority of their peak weight loss for an additional 10 months without meaningful regain.

That stability stands in contrast to many behavioral and even surgical weight-loss studies, where gradual regain of 20-30% of lost weight over years two through five is well documented in the obesity literature.

Cardiometabolic improvements

Weight loss was accompanied by meaningful changes in cardiometabolic risk markers:

| Marker | Semaglutide | Placebo | |---|---|---| | Waist circumference | −14.4 cm | −5.2 cm | | Systolic blood pressure | −5.7 mmHg | −1.6 mmHg | | C-reactive protein | −51.0% | −17.0% | | Triglycerides | −20.6% | −4.6% |

The reduction in C-reactive protein, a systemic inflammation marker, was particularly large and aligns with cardiovascular benefit signals later confirmed in the SELECT cardiovascular outcomes trial.

Safety profile over two years

Gastrointestinal events were the most common adverse effects, consistent with GLP-1 receptor agonist pharmacology:

| Adverse event | Semaglutide | Placebo | |---|---|---| | Nausea | 56.5% | 16.8% | | Diarrhea | 37.2% | 15.8% | | Vomiting | 28.6% | 6.9% | | Constipation | 31.2% | 9.9% |

Most gastrointestinal symptoms were mild to moderate and peaked during dose escalation (weeks 1-16). Symptom frequency dropped substantially after participants reached the maintenance dose, and few events led to permanent discontinuation.

Discontinuation rates differed between arms. About 13.5% of semaglutide-treated participants stopped treatment due to adverse events, compared with 4.0% in the placebo group. The trial completion rate was approximately 82% in the semaglutide arm and 72% in the placebo arm, which is respectable for a two-year obesity trial.

Gallbladder-related events, including cholelithiasis, occurred more frequently with semaglutide (4.5% vs 1.0%), consistent with the known association between rapid weight loss and gallstone formation. Pancreatitis was not reported, though the sample size was too small to draw conclusions about rare events.

Strengths of the trial

Duration. At 104 weeks, STEP-5 remains one of the longest placebo-controlled semaglutide weight-management trials. This matters because weight regain is the central challenge in obesity treatment, and most drug trials stop at 52 or 68 weeks.

Placebo control throughout. Unlike STEP-4, which withdrew the drug at week 20 to measure rebound, STEP-5 kept both arms on their assigned treatment for the full two years. This design directly tests the question patients and clinicians actually care about: what happens if I stay on this medication long-term?

Lifestyle counseling in both arms. Both groups received the same behavioral support, isolating the pharmacological contribution of semaglutide.

Limitations worth knowing

Small sample. With 304 participants, STEP-5 is substantially smaller than STEP-1 (n = 1,961) or STEP-3 (n = 611). The smaller sample increases uncertainty around point estimates and limits the ability to detect rare adverse events. The confidence intervals around the primary endpoint are wider than those in the larger STEP trials.

Limited diversity. The population was predominantly white and female. Whether the same degree of weight loss applies across different racial, ethnic, and sex subgroups cannot be confirmed from this trial alone.

No diabetes cohort. Patients with type 2 diabetes were excluded. STEP-2 addressed that population separately, finding somewhat lower weight loss (approximately 9.6% at 68 weeks), likely because insulin resistance and diabetes medications blunt weight-loss responses.

Industry-funded. Novo Nordisk funded STEP-5 and was involved in trial design, data collection, and statistical analysis. While this is standard practice for registration trials, it is a conflict of interest readers should weigh.

No data after drug withdrawal. STEP-5 did not include a post-treatment follow-up period. STEP-1 extension data and the separate STEP-4 trial both showed that patients regain roughly two-thirds of lost weight within one year of stopping semaglutide. STEP-5 cannot speak to what happens after discontinuation, which is a significant gap given that current evidence suggests indefinite treatment is necessary to maintain results.

What this means for clinical practice

STEP-5 answered its core question clearly: semaglutide 2.4 mg maintains weight loss through at least two years of continuous use. The drug does not appear to lose effectiveness over this time horizon. For patients and prescribers considering long-term anti-obesity pharmacotherapy, that durability signal was a necessary piece of the evidence base before committing to ongoing treatment.

The American Gastroenterological Association's 2022 clinical practice guideline recommends long-term pharmacotherapy for patients with obesity, framing these medications as chronic treatments rather than short courses. STEP-5's two-year data supports that framing with controlled evidence rather than clinical assumption.

The practical implication is straightforward: patients who respond well to semaglutide 2.4 mg and tolerate the gastrointestinal side effects can expect their weight loss to remain stable through at least year two, as long as they continue the medication and maintain lifestyle modifications. Whether that durability extends to years three, four, and five is not yet established in controlled settings, though post-marketing surveillance and real-world studies are beginning to fill that gap.

Cost and access remain the largest barriers to translating STEP-5's findings into population-level benefit. At a list price exceeding $1,300/month for Wegovy, the question is less whether the drug works and more whether health systems and insurers will cover it long enough for patients to realize the sustained benefits this trial demonstrated.

Frequently asked questions

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References

1. Garvey WT, Batterham RL, Bhatta M, et al. Two-year effects of semaglutide in adults with overweight or obesity: the STEP 5 trial. Nature Medicine. 2022;28(10):2083-2091. PubMed
2. Wilding JPH, Batterham RL, Calanna S, et al. Once-weekly semaglutide in adults with overweight or obesity (STEP 1). N Engl J Med. 2021;384(11):989-1002. PubMed
3. 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
4. Wegovy (semaglutide) prescribing information. Novo Nordisk. Revised 2023. FDA Label
5. Amaro A, Sugimoto D, Cusi K. American Gastroenterological Association guideline on pharmacological interventions for adults with obesity. Gastroenterology. 2022;163(5):1198-1225. PubMed