Semaglutide: Ozempic, Wegovy & the math

What semaglutide is

Semaglutide is a synthetic analogue of the gut hormone glucagon-like peptide-1 (GLP-1), made by Novo Nordisk. It activates the GLP-1 receptor, which enhances glucose-dependent insulin secretion, suppresses glucagon, slows gastric emptying, and acts on appetite centres in the brain to reduce hunger and food intake. It is a single-receptor agonist — in contrast to tirzepatide (dual GLP-1/GIP) and retatrutide (triple GLP-1/GIP/glucagon).

The molecule is engineered for a long duration of action: a fatty-diacid chain on the peptide drives strong, reversible binding to albumin, which slows clearance and protects it from enzymatic degradation. That is why the injectable form is dosed once weekly. An oral tablet form (Rybelsus, and an oral Wegovy approved December 2025) uses an absorption enhancer and is dosed daily.

The brands

• Ozempic — subcutaneous, for type 2 diabetes (also CV-risk reduction). Doses 0.25 / 0.5 / 1 / 2 mg weekly.
• Wegovy — subcutaneous, for weight management, up to 2.4 mg weekly; also carries cardiovascular and MASH (liver) indications. An oral Wegovy tablet (25 mg daily) was approved December 2025 — the first oral GLP-1 for weight loss.
• Rybelsus — oral tablet (7 / 14 mg daily), for type 2 diabetes.

All three are the same active ingredient. The differences are indication, formulation (injectable vs oral) and maximum dose — not the molecule.

What the trials showed

In the STEP-1 obesity trial (NEJM 2021; ~1,961 participants), adults on semaglutide 2.4 mg weekly alongside lifestyle intervention lost a mean of 14.9% of body weight over 68 weeks, versus 2.4% on placebo; 86% reached at least 5% loss. In the SELECT cardiovascular outcomes trial (NEJM 2023; ~17,600 participants with established cardiovascular disease and overweight/obesity but no diabetes), semaglutide 2.4 mg reduced major adverse cardiovascular events by about 20% (hazard ratio 0.80) over a mean ~40 months — the basis for its cardiovascular indication.

More recent readouts extended the picture: the OASIS-4 trial of oral semaglutide 25 mg reported roughly 16.6% mean weight loss over 64 weeks (supporting the oral Wegovy approval), and the ESSENCE trial supported a MASH (fatty-liver) indication. These figures are published trial outcomes for specific protocol doses under medical supervision — cited as facts, not as targets.

Tolerability is dominated by gastrointestinal effects (nausea, vomiting, diarrhoea, constipation), generally mild-to-moderate, dose-related, and most pronounced during titration. Semaglutide carries a boxed warning for thyroid C-cell tumours (rodent data) and is contraindicated with a personal/family history of medullary thyroid carcinoma or MEN 2. Read the primary sources at the foot of this page rather than relying on this summary.

The titration ladders

These are the approved label schedules, listed as facts — the slow ramp exists because side effects concentrate during escalation, and because a ~1-week half-life means each step takes ~4–5 weeks to fully express:

Ozempic (diabetes) follows a shorter ladder — 0.25 mg for 4 weeks, then 0.5 mg, then up to 1 mg and a 2 mg maximum, never escalating faster than every 4 weeks.

The math

Approved pens are pre-dosed, so the arithmetic only matters if you are dealing with a compounded or lyophilized vial that must be reconstituted — the same arithmetic the peptide reconstitution calculator does for any vial. Worked example, presented purely as arithmetic:

Concentration is just milligrams divided by millilitres, and units are just hundredths of a millilitre on a U-100 insulin syringe. Change the water volume and every number moves: the same 5 mg vial with 1 mL gives 5 mg/mL (so 0.25 mg = 5 units), while 2.5 mL gives 2 mg/mL. The reconstitution calculator converts vial size + water + target into exact syringe units (and works in reverse). None of this implies a dose you should take; it is the conversion math for whatever a clinician specifies.

Half-life & what a weekly schedule means

Semaglutide's elimination half-life is about one week (≈165–184 hours), driven by >99% albumin binding. A ~1-week half-life is what makes once-weekly injection viable: when the next dose is due, roughly half the prior dose remains, so levels stack toward a plateau rather than spiking and crashing. With weekly dosing the concentration climbs for about 4–5 weeks before it stabilizes at steady state — which is why titration steps are spaced ~4 weeks apart and why effects (and side effects) at a new dose aren't fully expressed in week one. You can see this accumulation curve for any half-life and interval in the half-life visualizer.

Storage & handling

• Approved pens (Ozempic / Wegovy): stored refrigerated at 2–8°C (36–46°F); once in use, kept per the label's room-temperature window. Follow the pen's own instructions.
• Lyophilized (powder, unreconstituted): for compounded vials, freeze-dried peptide is the most stable form and is typically stored cold and away from light.
• Reconstituted (in bacteriostatic water): refrigerated at 2–8°C, not frozen — freeze/thaw cycles can damage peptide bonds. Published stability practice assigns GLP-class peptides in bacteriostatic water a beyond-use window of roughly four weeks.
• BUD honesty: a "beyond-use date" is a stability convention, not a sterility guarantee. With unregulated compounded material, neither label accuracy nor sterility can be assumed.

Tracking semaglutide in OptiPin

Whether you're on a prescribed Ozempic/Wegovy pen or tracking a weekly GLP-class compound, OptiPin treats it like any other entry:

• Dose log + weekly reminders — record each injection on a once-weekly cadence and get reminded on the due day, with site rotation.
• Titration schedule — set the 0.25 → 0.5 → 1.0 → 1.7 → 2.4 mg ramp and OptiPin tracks which step you're on and when the next is due.
• Weight & body metrics — log weight and measurements and see them plotted directly over your dose timeline.
• OptiInsight analysis — OptiPin's AI reads the full record (doses, weight, symptoms, labs) and surfaces what moved with what.
• Pen & vial tracking — log the pen or reconstituted vial; OptiPin estimates remaining doses and an empty date, and warns before you run out.