Ozempic and Weight Loss: Trial Data, Expected Results, and Clinical Considerations

The SUSTAIN clinical programme evaluated semaglutide at doses of 0.5 mg and 1 mg in patients with type 2 diabetes. Weight loss was a secondary endpoint in these trials, not the primary outcome.

Key weight loss data from SUSTAIN trials:

• SUSTAIN 1 (monotherapy, 30 weeks): semaglutide 0.5 mg produced mean weight loss of 3.7 kg; 1 mg produced 4.5 kg versus 1.0 kg for placebo
• SUSTAIN 2 (vs sitagliptin, 56 weeks): semaglutide 1 mg group lost 6.1 kg compared to 1.9 kg with sitagliptin
• SUSTAIN 6 (cardiovascular outcomes, 104 weeks): semaglutide 1 mg group lost 4.9 kg versus 0.5 kg for placebo
• SUSTAIN 7 (vs dulaglutide, 40 weeks): semaglutide 1 mg group lost 6.5 kg versus 3.0 kg for dulaglutide 1.5 mg

These results demonstrate consistent weight reduction across different comparators.

The magnitude of weight loss with Ozempic (1 mg) is greater than most other GLP-1 receptor agonists at their licensed diabetes doses.

The STEP programme, which tested semaglutide 2.4 mg (Wegovy) specifically for weight management, showed larger reductions: approximately 15% of body weight over 68 weeks.

This higher dose is licensed separately for obesity treatment.

Semaglutide produces weight loss through several overlapping physiological mechanisms. Understanding these helps explain why the effect varies between individuals.

Central appetite suppression:

Semaglutide crosses the blood-brain barrier and acts on GLP-1 receptors in the hypothalamus and brainstem. This reduces hunger signals and increases satiety after meals.

Functional MRI studies demonstrate reduced activation in brain regions associated with food reward and craving.

Delayed gastric emptying:

GLP-1 receptor activation slows gastric motility, meaning food remains in the stomach longer. Patients feel full sooner and for longer after eating.

This effect is most pronounced at the start of treatment and partially attenuates over time.

Reduced energy intake:

Metabolic ward studies show that patients on semaglutide spontaneously reduce caloric intake by approximately 20 to 35% without conscious dietary restriction.

This caloric deficit is the primary driver of weight loss.

Effects on food preference:

Emerging data suggest semaglutide shifts food preferences away from high-fat, energy-dense foods.

Patients frequently report reduced cravings for fatty and sugary foods, though this has not been fully characterised in controlled trials.

Metabolic rate considerations:

Weight loss from semaglutide, like any weight loss, produces some adaptive thermogenesis (reduced resting energy expenditure).

This metabolic adaptation may partly explain weight loss plateaus typically seen after 6 to 9 months of treatment.

Weight loss with Ozempic follows a predictable pattern linked to the dose titration schedule and physiological adaptation.

Weeks 1 to 4 (0.25 mg dose):

Minimal weight change expected. This is the titration phase. Some patients lose 0.5 to 1 kg from reduced appetite, but the low dose is not optimised for weight reduction.

Weeks 5 to 8 (0.5 mg dose):

Appetite suppression becomes more noticeable. Most patients begin losing weight at a rate of 0.5 to 1 kg per week.

GI side effects, particularly nausea, contribute to reduced food intake during this phase.

Weeks 9 to 16 (0.5 mg or 1 mg dose):

Steady weight loss continues. If escalated to 1 mg, a further reduction in appetite typically occurs. Patients on 1 mg lose weight more rapidly than those remaining at 0.5 mg.

Months 4 to 9:

Peak weight loss velocity. Most patients achieve the majority of their total weight loss during this window. Body composition changes become visually apparent.

Months 9 to 12 and beyond:

Weight loss slows and often plateaus. This is normal and reflects metabolic adaptation, not treatment failure. The drug continues to work by preventing weight regain.

SUSTAIN data show weight is maintained while treatment continues.

• Average total weight loss at 12 months on Ozempic 1 mg: 5 to 7% of baseline body weight
• Approximately 30 to 40% of patients lose more than 5% of their body weight
• Around 10 to 15% of patients lose more than 10% of body weight

Clinical trial averages mask substantial individual variation. Several factors predict whether a patient will respond strongly or modestly to Ozempic for weight loss.

Baseline BMI and metabolic status:

Patients with higher baseline BMI tend to lose more absolute weight but a similar percentage of body weight.

Those with insulin resistance (higher fasting insulin, higher HOMA-IR) often respond well because semaglutide addresses the underlying metabolic dysfunction.

Dietary behaviour and caloric intake:

Ozempic reduces appetite, but patients who combine it with structured dietary changes (e.g.

reduced refined carbohydrate intake, portion control) consistently achieve greater weight loss than those who rely on the drug alone.

Physical activity:

Exercise does not dramatically accelerate weight loss on Ozempic but preserves lean muscle mass, which is critical for long-term metabolic health.

Resistance training at least twice per week is recommended by NICE.

Dose achieved:

Patients who tolerate and remain on 1 mg lose more weight than those who stay at 0.5 mg due to side effects.

Genetics and GLP-1 receptor sensitivity:

Emerging pharmacogenomic data suggest that polymorphisms in the GLP-1 receptor gene influence individual response. This field is not yet clinically actionable.

Concomitant medications:

Some medications promote weight gain (insulin, sulfonylureas, mirtazapine, certain antipsychotics). These may partially offset semaglutide's weight-lowering effect.

Semaglutide is marketed under two brand names in the UK, and the distinction matters for prescribing, licensing, and reimbursement.

Ozempic (semaglutide 0.25 mg, 0.5 mg, 1 mg):

• Licensed indication: type 2 diabetes mellitus as an adjunct to diet and exercise
• Weight loss is a secondary benefit, not the licensed purpose
• Available on NHS prescription for patients meeting NICE NG 28 criteria for GLP-1 therapy in diabetes
• Prescribing Ozempic solely for weight loss in non-diabetic patients is off-label use

Wegovy (semaglutide 2.4 mg):

• Licensed indication: weight management in adults with BMI of 30 kg/m2 or greater, or 27 kg/m2 or greater with at least one weight-related comorbidity
• NICE TA 875 approved Wegovy for NHS use in specialist weight management services (from June 2023)
• Higher dose provides greater weight loss: approximately 15% of body weight at 68 weeks in the STEP 1 trial
• Separate titration schedule over 16 weeks, reaching the 2.4 mg maintenance dose

Supply considerations:

Both Ozempic and Wegovy have experienced intermittent supply issues in the UK since 2022. Novo Nordisk has issued supply notifications through the DHSC.

Patients should not switch between the two products without prescriber involvement, as the doses and indications differ.

Weight regain after discontinuing semaglutide is well documented and represents one of the most important clinical considerations for patients and prescribers.

STEP 1 extension data:

Patients who stopped semaglutide 2.4 mg after 68 weeks regained approximately two-thirds of their lost weight within 12 months of discontinuation.

Hunger and caloric intake returned to pre-treatment levels within weeks of stopping.

Mechanisms of weight regain:

• Appetite suppression ceases as semaglutide plasma levels decline (half-life 7 days, effectively cleared within 5 weeks)
• Metabolic adaptations from weight loss persist, meaning resting energy expenditure remains lower than predicted for the patient's new weight
• Hormonal hunger signals (ghrelin, peptide YY) revert to pre-treatment patterns

Clinical implications:

• Patients should be counselled before starting that weight loss with Ozempic typically requires ongoing treatment
• If stopping is planned (e.g. pregnancy planning), structured dietary support and exercise programmes should be in place before discontinuation
• NICE does not currently specify a maximum treatment duration for GLP-1 agonists in diabetes, supporting long-term use
• Some patients maintain partial weight loss through sustained dietary and exercise habits developed during treatment

A realistic conversation about long-term treatment expectations at initiation helps manage patient expectations and improves adherence.