What it is

Semaglutide is a GLP-1 analogue with 94% sequence homology to human GLP-1 [1]. Its peptide backbone is made by yeast fermentation, and a C18 fatty diacid attached at position 26 lets it bind albumin, which is the main reason it lasts about a week in the body [1]. A second change at position 8 protects it from the enzyme DPP-4 [1]. Novo Nordisk sells it in the US under three names. Ozempic is a once-weekly injection for adults with type 2 diabetes [1]. Wegovy is a once-weekly injection for weight reduction, cardiovascular risk reduction, and noncirrhotic MASH with moderate to advanced fibrosis [2]. Rybelsus is a daily tablet for type 2 diabetes, co-formulated with an absorption enhancer because oral bioavailability is only about 0.4 to 1% [3]. Injectable doses are written in milligrams, which is how STACK logs them.

How it works

Semaglutide selectively binds and activates the GLP-1 receptor, the same target as the body’s own GLP-1 [1]. GLP-1 is a physiological hormone with multiple actions on glucose, and semaglutide lowers both fasting and after-meal blood glucose and reduces body weight [1]. It also delays early after-meal gastric emptying, which slows how fast glucose enters the blood and can change the absorption of other oral medicines [1]. The long duration comes from protraction: albumin binding reduces renal clearance and shields the molecule from breakdown, and the DPP-4-resistant backbone adds further stability [1]. Absolute bioavailability after subcutaneous injection is 89%, peak concentration arrives 1 to 3 days after a dose, and exposure is similar from the abdomen, thigh or upper arm [1].

What the evidence shows

STEP 1 (NEJM 2021) enrolled 1,961 adults with obesity, or overweight with a weight-related condition, and no diabetes. Participants received semaglutide 2.4 mg once weekly or placebo for 68 weeks plus lifestyle intervention; mean weight change was -14.9% versus -2.4%, and 86.4% versus 31.5% lost at least 5% of body weight [4]. SUSTAIN-6 (NEJM 2016) followed 3,297 adults with type 2 diabetes at high cardiovascular risk for 104 weeks; the composite of cardiovascular death, nonfatal heart attack or nonfatal stroke occurred in 6.6% on semaglutide versus 8.9% on placebo (hazard ratio 0.74), with higher rates of retinopathy complications [5]. SELECT (NEJM 2023) enrolled 17,604 adults with cardiovascular disease and overweight or obesity but no diabetes; the same composite occurred in 6.5% versus 8.0% (hazard ratio 0.80) over a mean follow-up of 39.8 months [6].

Regulatory status

Semaglutide is an FDA-approved drug. Ozempic was first approved in 2017 for glycemic control in adults with type 2 diabetes and to reduce major adverse cardiovascular events in adults with type 2 diabetes and cardiovascular disease [1]. The Wegovy label revised 08/2025 lists three indications: cardiovascular risk reduction in adults with cardiovascular disease and obesity or overweight; weight reduction in adults and pediatric patients aged 12 and older with obesity, or adults with overweight plus a comorbid condition; and noncirrhotic MASH with moderate to advanced fibrosis (accelerated approval) [2]. Rybelsus is approved for type 2 diabetes [3]. On May 1 2026 FDA proposed not to include semaglutide on the 503B bulks list; comments closed Jun 30 2026 [7]. FDA states that salt forms such as semaglutide sodium and acetate are different active ingredients from the approved drug and that it had received 990 adverse event reports for compounded semaglutide as of May 31 2026 [8].

Half-life and what it means for a level curve

The Ozempic label reports an elimination half-life of approximately 1 week in adults with type 2 diabetes after subcutaneous injection, and notes that semaglutide stays in the circulation for about 5 weeks after the last dose [1]. The Wegovy label gives the same approximately 1 week in adults with obesity or overweight, with the drug present for about 5 to 7 weeks after a last dose of 2.4 mg [2]. The Rybelsus label also states approximately 1 week for the oral tablet [3]. The reference half-life in STACK is 168 hours. Because the half-life equals the 7-day dosing interval, each weekly injection lands when roughly half of the previous one remains, so the curve stacks smoothly and shows only a mild weekly ripple. With regular dosing a level reaches about 97% of steady state after about 5 half-lives, here roughly 5 weeks. STACK’s curve is an estimate from this published half-life, not a blood level.

Reported side effects

In placebo-controlled type 2 diabetes trials, the most common adverse reactions with Ozempic were nausea (15.8 to 20.3% versus 6.1% on placebo), vomiting (5.0 to 9.2% versus 2.3%), diarrhea (8.5 to 8.8% versus 1.9%), abdominal pain and constipation [1]. In the Wegovy weight-reduction trials, nausea was reported by 44% (16% placebo), diarrhea by 30% (16%), vomiting by 24% (6%), constipation by 24% (11%), abdominal pain by 20% (10%) and headache by 14% [2]. In STEP 1, nausea and diarrhea were typically transient and mild to moderate; 4.5% stopped treatment because of gastrointestinal events versus 0.8% on placebo [4]. All three labels carry a boxed warning: semaglutide causes thyroid C-cell tumors in rodents, human relevance is unknown, and it is contraindicated with a personal or family history of medullary thyroid carcinoma or MEN 2 [2]. Other warnings include acute pancreatitis, gallbladder disease, hypoglycemia, acute kidney injury and pulmonary aspiration during anesthesia [2]. Tell your prescriber about anything unexpected.

Storage and handling

Before first use, store Ozempic in a refrigerator at 2°C to 8°C (36°F to 46°F), not in the freezer or against the cooling element; do not use it if it has been frozen [1]. After first use, the Ozempic pen can be kept for 56 days at room temperature (15°C to 30°C) or in the refrigerator, with the cap on, protected from excessive heat and sunlight, and then discarded even if medicine remains [1]. Wegovy is a single-dose pen: refrigerate it in the original carton, keep it from light, and if needed it can stay at 8°C to 30°C for up to 28 days before the cap is removed; discard after use [2]. Rybelsus tablets are taken by mouth and need no refrigeration handling of this kind [3]. Both injectable products are ready-to-use solutions. If your prescriber gave you a product that requires reconstitution, STACK’s reconstitution calculator handles the volume arithmetic; it does not suggest amounts.

What STACK tracks for it

STACK logs each semaglutide dose as your prescriber wrote it, in milligrams for injections, with the date and time, and it can log Rybelsus tablets as daily entries. It draws an estimated level curve from the 168-hour reference half-life, which is useful for seeing how slowly levels drift down after a missed or delayed dose. It stores the escalation schedule your prescriber gave you so you can see where you are on it, without proposing one. You can record the injection site for each dose across the abdomen, thigh and upper arm [1]. Weight, side effects and how long they lasted, and pen inventory are tracked alongside, including a 56-day countdown for an opened Ozempic pen [1]. STACK shows your data; it never prescribes.

The reference half-life in STACK

STACK's simulator and the app use 168 h (7 days) for Semaglutide: approximately 1 week (about 168 h); the Ozempic, Wegovy and Rybelsus labels all state this value. Measured in: adults with type 2 diabetes (Ozempic label) and adults with obesity or overweight (Wegovy label), subcutaneous.

Semaglutide

168 h (7 days)

Reference half-life from published pharmacokinetics; editable. Educational only — not medical or dosing advice.

“With an elimination half-life of approximately 1 week, semaglutide will be present in the circulation for about 5 weeks after the last dose.” — OZEMPIC (semaglutide) injection — Full Prescribing Information, §12.3 Elimination (2023 revision). U.S. FDA / Novo Nordisk. View source

Simulate Semaglutide Plan with Semaglutide

Estimate only. Modelled from the published half-life you selected and the doses you logged — not a measured blood level. Do not use it to make medication decisions.

Free tools for Semaglutide

Sources

Every URL below was fetched and checked on 2026-09-24. Bracketed numbers in the text link here.

Semaglutide

What it is

How it works

What the evidence shows

Regulatory status

Half-life and what it means for a level curve

Reported side effects

Storage and handling

What STACK tracks for it

The reference half-life in STACK

Semaglutide

Free tools for Semaglutide

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Sources