The semaglutide is a GLP-1 analogue, the incretin the gut releases after a meal. It binds to the GLP-1 receptor, slows stomach emptying and strengthens the satiety signal. Its chain has been modified to stay in the blood for a long time: it is taken once a week, on the same day, and not every day.
Wegovy is the name of the Novo Nordisk medicine that uses this molecule, in a fixed-dose pen. The PeptidLab vial is a research lyophilizate. It has neither the pen device, nor its excipient, nor the status of the medicine. The name in brackets on the label is there to place the molecule, not to sell the pen.
The schedule, step by step
The STEP 1 trial (Wilding et al., New England Journal of Medicine, 2021) and the Wegovy label describe the same escalation. No step is skipped.
- Weeks 1 to 4 : 0.25 mg, once a week.
- Weeks 5 to 8 : 0.5 mg.
- Weeks 9 to 12 : 1 mg.
- Weeks 13 to 16 : 1.7 mg.
- From week 17 : 2.4 mg, the label's maintenance dose.
The starting step is not "the small dose to see". It gives the digestive tract time to adjust. In trials, nausea is the most common reason for holding a step longer, not for jumping up. The full table, with the syringe, is on the protocol sheet.
Read the vial, not the pen label
5 mg, 10 mg, 20 mg or 30 mg is the mass of powder in the vial. It is not the weekly dose. A 30 mg vial contains much more than 2.4 mg: it is used to prepare a solution, then to draw the volume for the step.
Reconstitutions used on the product page:
- 5 mg in 2 mL → 2.5 mg/mL. At this concentration, 0.25 mg is 0.10 mL, i.e. 10 units on a U-100 syringe.
- 10 mg in 2 mL → 5 mg/mL. 0.25 mg is 0.05 mL.
- 20 mg in 2 mL → 10 mg/mL.
- 30 mg in 3 mL → 10 mg/mL.
The solvent volume is chosen so that the syringe mark falls on a readable graduation, not to empty the vial in one go. The product page's Apply button loads these figures into the calculator.
Where it sits among the other agonists
Semaglutide activates only the GLP-1 receptor. Tirzepatide activates two, GLP-1 and GIP. R3TA activates three, adding glucagon. This is not a "strength" scale: they are three molecules, three schedules, three product pages. The details are in the guide to the three agonists.
Holding the step, then storing the vial
The day stays the same from one week to the next. If a dose is missed, the next one is not doubled: semaglutide stays in the blood for a long time, which is the principle of weekly dosing, and two close doses catch nothing up. You resume the current step on the usual day.
The powder is kept between 2 and 8 °C, away from light, in its original packaging. Once reconstituted, so is the solution, with the date written on the label. On these product pages, the shelf life after reconstitution is up to 28 to 30 days. A reconstituted solution is not frozen, and the vial is not left out of the cold longer than the draw.
Frequently asked questions
Are Wegovy and this vial the same product?
No. Wegovy is a fixed-dose medicine in a pen. The vial is a research lyophilizate: the mass shown is used to calculate a concentration, not to replace the pen.
Why not start at 2.4 mg?
Because the published schedule goes up in four-week steps. 2.4 mg is the maintenance dose, not the starting dose.
How many weeks does a 30 mg vial correspond to?
Nothing fixed. 30 mg is the powder in the vial. The weekly dose is read in the table, from 0.25 mg to 2.4 mg, then converted into volume according to the chosen dilution.
Can the injection day change?
The schedule keeps the same day every week. If there is a delay, the next dose is not doubled to "catch up".
Fact sheet
- Last name
- Semaglutide
- Family
- Long-acting GLP-1 analogue
- Structure
- 31 amino acids, C18 fatty acid chain
- Molar mass
- 4 113,6 g/mol
- N° CAS
- 910463-68-2
- Published half-life
- About 7 days
- Developer
- Novo Nordisk
- Regulatory status
- Authorised medicine (Ozempic, Wegovy). The PeptidLab vial is not this medicine.
What the research says
Summary of published data, written by the PeptidLab team. It describes molecules studied in the laboratory or in clinical trials: nothing here is an indication for use.
2016Phase 3N Engl J Med
SUSTAIN-6: 3,297 patients with type 2 diabetes at high cardiovascular risk. Major cardiovascular events were less frequent on semaglutide than on placebo (6.6% vs 8.9%).
2021Phase 3N Engl J Med
STEP 1: 1,961 adults with overweight or obesity, 2.4 mg a week for 68 weeks. Average weight loss of 14.9%, versus 2.4% on placebo.
2022Phase 3Diabetes Obes Metab
STEP 1 extension: one year after stopping treatment, participants had regained about two thirds of the weight lost.
2023Phase 3N Engl J Med
SELECT: 17,604 adults with overweight or obesity and cardiovascular disease, without diabetes. The risk of major cardiovascular events fell by 20% compared with placebo.
Safety: what studies report
- The most common adverse effects in the trials are digestive: nausea, diarrhoea, vomiting and constipation, especially during dose escalation.
- The package leaflets also mention pancreatitis, gallbladder disorders and, in rodents, thyroid C-cell tumours whose relevance to humans has not been established.
Sources
Links to PubMed or to the original document. Articles in English.
- Marso SP et al. Semaglutide and Cardiovascular Outcomes in Patients with Type 2 Diabetes. N Engl J Med, 2016. PubMed
- Wilding JPH et al. Once-Weekly Semaglutide in Adults with Overweight or Obesity. N Engl J Med, 2021. PubMed
- Wilding JPH et al. Weight regain and cardiometabolic effects after withdrawal of semaglutide: the STEP 1 trial extension. Diabetes Obes Metab, 2022. PubMed
- Lincoff AM et al. Semaglutide and Cardiovascular Outcomes in Obesity without Diabetes. N Engl J Med, 2023. PubMed
Updated October 2026.
This guide has an informative and scientific purpose. PeptidLab products are intended exclusively for laboratory research and are not intended for human or animal consumption.