What is Semaglutide?
Semaglutide is a GLP-1 receptor agonist — a synthetic analogue of glucagon-like peptide-1, an incretin hormone produced in the intestine in response to food. Originally developed for type 2 diabetes management (marketed as Ozempic), it gained approval for chronic weight management at higher doses (marketed as Wegovy).
In the research peptide context, Semaglutide is used at similar doses to clinical protocols, primarily for appetite suppression and metabolic improvement.
Mechanism of Action
GLP-1 receptors are found throughout the body, but Semaglutide's weight management effects come primarily from three sites:
- Hypothalamus — GLP-1 receptors in the arcuate nucleus and other appetite-regulating regions reduce hunger signals and increase satiety. This is the dominant mechanism for weight loss.
- Gastric emptying — Semaglutide slows stomach emptying, prolonging the feeling of fullness after meals.
- Pancreas — Stimulates glucose-dependent insulin secretion and suppresses glucagon — beneficial for blood sugar control but not primary to weight loss.
Clinical Efficacy
The STEP trials (Semaglutide Treatment Effect in People with obesity) demonstrated remarkable results:
- STEP 1: 2.4 mg/week for 68 weeks produced mean weight loss of 14.9% of body weight vs 2.4% for placebo
- STEP 4: Patients who discontinued Semaglutide regained most lost weight within 1 year, confirming ongoing treatment is required to maintain results
- Improvements in cardiovascular risk markers, blood pressure, and HbA1c were also observed
Protocol
Semaglutide is administered via subcutaneous injection once weekly. Dose titration is essential to minimise gastrointestinal side effects:
- Week 1–4: 0.25 mg/week
- Week 5–8: 0.5 mg/week
- Week 9–12: 1.0 mg/week
- Week 13–16: 1.7 mg/week
- Week 17+: 2.4 mg/week (maintenance)
Many users find effective appetite suppression at lower doses (0.5–1.0 mg/week) and choose not to titrate to the maximum. Starting too high too quickly is the primary cause of nausea and vomiting.
Half-Life and Dosing Rationale
Semaglutide has a half-life of approximately 7 days — the longest of any GLP-1 agonist. This allows once-weekly dosing while maintaining very stable serum levels (low peak-to-trough ratio). The extended half-life is achieved through albumin binding (similar to the DAC modification in CJC-1295).
Side Effects
The most common side effects are gastrointestinal and typically occur early in treatment:
- Nausea (44% of participants in STEP 1)
- Vomiting, diarrhoea, constipation
- Reduced appetite (often desired)
These typically resolve after 4–8 weeks as the body adjusts. Slow dose titration significantly reduces their severity.
Rarer but serious concerns include pancreatitis risk and, in rodent studies, thyroid C-cell tumours (though this has not been observed in humans at therapeutic doses).
Combination with Tesamorelin
An interesting combination gaining attention is Semaglutide with Tesamorelin — a GHRH analogue specifically studied for visceral fat reduction. While Semaglutide primarily reduces overall body weight through appetite suppression, Tesamorelin targets visceral adipose tissue through GH-mediated lipolysis. The two mechanisms are complementary, and the combination may produce superior body composition outcomes compared to either alone.
However, this combination requires careful monitoring as both agents affect glucose metabolism and lipid profiles.