Semaglutide Quick Start
Semaglutide is a 31-amino-acid GLP-1 analog stabilised against DPP-4 degradation by an Aib substitution and acylated with a C18 diacid chain, giving it a roughly one-week half-life. It is the most extensively studied molecule in its class and is dosed once weekly with a slow, deliberate step-up.
This guide is an educational research reference. It does not diagnose, treat, or prescribe, and is not medical advice. Consult a licensed clinician before considering any compound.
Semaglutide Dosing Protocol
Semaglutide is dosed once weekly, stepping up roughly every four weeks. The doses below mirror the titration schedule used for the approved molecule and are shown as research context, not a personal dosing recommendation. Note the milligram figures are an order of magnitude smaller than tirzepatide's — the two are not interchangeable.
Injection — Subcutaneous
| Step | Weekly dose | Typical duration |
|---|---|---|
| 1 (start) | 0.25 mg | 4 weeks |
| 2 | 0.5 mg | 4 weeks |
| 3 | 1 mg | 4 weeks |
| 4 | 1.7 mg | 4 weeks |
| 5 (max) | 2.4 mg | Maintenance |
Semaglutide Reconstitution Guide
Semaglutide's microgram-to-low-milligram doses make the reconstitution volume a readability decision as much as a chemistry one. A larger volume gives a bigger, easier-to-measure draw at the small early steps.
Injection
| BAC | Conc. | 0.25 mg | 2.4 mg |
|---|---|---|---|
| 2 mL | 10 mg/mL | 2.5 u | 24 u |
| 4 mL | 5 mg/mL | 5 u | 48 u |
Units are U-100 insulin-syringe units. Pick one volume and write it on the vial — the two conventions differ by a factor of two at every step.
Not interchangeable with tirzepatide
Semaglutide tops out at 2.4 mg weekly; tirzepatide runs to 15 mg. Reading a tirzepatide unit figure onto a semaglutide vial would be a six-fold overdose at the top step.
Reconstitution steps
- Inspect the vial. Confirm the label, expected milligram amount, and that the powder looks dry and intact.
- Wipe the stoppers. Use an alcohol swab on both the bacteriostatic water and peptide vial stoppers.
- Draw the chosen volume. 2 mL (or 4 mL for easier early steps) into the vial — this is the number that sets every concentration figure above.
- Inject down the wall. Release the water slowly down the inside wall, not directly onto the powder.
- Swirl, do not shake. Roll gently until dissolved. Shaking foams and can damage the peptide.
- Verify clarity. Solution should be clear and colorless. Discard if cloudy or particulate.
- Label and refrigerate. Note the date and volume added on the vial, then store at 2–8 °C. Do not freeze the reconstituted solution.
See the bacteriostatic water guide for diluent handling, or the reconstitution calculator to work any other volume.
How Semaglutide Works
Semaglutide is a GLP-1 receptor agonist. Activating that receptor increases glucose-dependent insulin secretion, suppresses glucagon, slows gastric emptying, and acts on hypothalamic appetite circuits. The Aib substitution resists DPP-4 breakdown and the fatty-acid chain binds albumin, together turning a native peptide with a two-minute half-life into a weekly molecule.
Incretin signaling
Glucose-dependent insulin release, so hypoglycaemia risk is low as a single agent.
Gastric emptying
Slowed transit contributes to satiety and to the GI effect profile.
Central appetite effects
Hypothalamic GLP-1 receptor activity is the basis for appetite endpoints.
Open question
Weight regain after discontinuation is well documented; durability without continued use is unresolved.
Who Should Avoid Semaglutide
The approved molecule has a large human safety dataset, but that does not transfer to research-grade material of unverified provenance. Categories where caution is most consistently flagged:
Personal or family MTC history
Rodent thyroid C-cell findings drive a boxed contraindication for the class, including MEN 2.
Pregnancy & lactation
Not established as safe; generally discontinued well ahead of a planned pregnancy.
History of pancreatitis
A recognised class-level adverse event and a standard trial exclusion.
Diabetic retinopathy
Rapid glycaemic improvement has been associated with transient retinopathy worsening in trial data.
Semaglutide Side Effects & Safety
Gastrointestinal effects
Nausea, vomiting, diarrhoea and constipation dominate, concentrated at initiation and after each step-up.
Gallbladder events
Reported across the class and associated with rapid weight reduction of any cause.
Injection-site reactions
Generally mild; rotate sites.
Quality-control risk
Identity and purity of research-grade material is a separate risk from the molecule — verify against a COA.
Timeline & What to Monitor
| Timeframe | Commonly tracked | Notes |
|---|---|---|
| Week 1–4 | Tolerability at 0.25 mg | A tolerability step, not a therapeutic one. |
| Week 4–16 | Response at each step-up | Four weeks per step is the published cadence. |
| Month 4–12 | Metabolic and body-composition endpoints | Trial endpoints are reported over this window. |
| After discontinuation | Regain trajectory | Documented in extension studies; plan for it. |
Semaglutide Evidence Context
SUSTAIN / STEP programmes
Large randomised programmes underpin the glycaemic and weight indications.
Cardiovascular outcomes
Outcome trials in this class have reported cardiovascular findings; read the specific trial.
Head-to-head
Compared directly against tirzepatide, with the dual agonist reporting larger mean reductions.
Open question
Durability after stopping remains the most consistently reported limitation.
Storage & Handling
| State | Storage | Notes |
|---|---|---|
| Lyophilized (powder) | −20 °C, protected from light | More stable than reconstituted solution. |
| Reconstituted (liquid) | 2–8 °C | Short-term; −20 °C for longer per the listing. |
| Appearance | Clear, colorless | Discard cloudy or particulate solutions. |
Semaglutide vs Tirzepatide vs Retatrutide
| Feature | Semaglutide | Tirzepatide | Retatrutide |
|---|---|---|---|
| Receptors | GLP-1 | GIP + GLP-1 | GIP + GLP-1 + glucagon |
| Max step referenced | 2.4 mg | 15 mg | 12 mg |
| Status | Approved molecule | Approved molecule | Investigational (Phase 3) |
| Page | This page | Tirzepatide | Retatrutide |
Frequently Asked Questions
How is semaglutide dosed?
Once weekly, starting at 0.25 mg and stepping up roughly every four weeks to a maximum of 2.4 mg. At 10 mg/mL that is 2.5 → 24 units on a U-100 syringe.
Why is the opening dose so hard to measure?
At 10 mg/mL, 0.25 mg is 2.5 units. Reconstituting the 20 mg vial to 4 mL instead gives 5 mg/mL, doubling every draw and making the early steps far easier to read accurately.
Can I use tirzepatide unit figures?
No. The two run on completely different milligram scales — 2.4 mg versus 15 mg at the top step. Reading across would be a large overdose.
How many doses are in a 20 mg vial?
At the 0.25 mg starting step, 80. At the 2.4 mg maintenance step, roughly 8.
Are there legal restrictions?
GLP-1-class research peptides may be subject to state-level restrictions — California, New York, Mississippi and Tennessee are flagged on the product listing. Verifying local compliance is the buyer's responsibility.
Is this page medical advice?
No. It is an educational research reference and does not diagnose, treat, or prescribe. Consult a licensed clinician before considering any compound.
Semaglutide Formats & Sourcing
Semaglutide is supplied as a lyophilized powder in a single 20 mg vial size. There is no pre-reconstituted pen or spray format for this compound. Batch-specific Certificates of Analysis are issued per lot.
| Format | Supplied as |
|---|---|
| Vial | 20 mg lyophilized powder |
Strengths are listed as sold; confirm against the product page and the batch COA before calculating anything.
Reference material for this protocol, with batch COA:
View Semaglutide on Spyro Peptides →References
- Marso SP, et al. Semaglutide and cardiovascular outcomes in type 2 diabetes (SUSTAIN-6). N Engl J Med (2016).
- Wilding JPH, et al. Once-weekly semaglutide in adults with overweight or obesity (STEP 1). N Engl J Med (2021).
- Frías JP, et al. Tirzepatide versus semaglutide once weekly. N Engl J Med (2021).
- Lau J, et al. Discovery of the once-weekly GLP-1 analogue semaglutide. J Med Chem (2015).
- Product listing regulatory note, spyropeptides.com — state-level restrictions for GLP-1-class research peptides.