Questions
Semaglutide questions, answered from the published record.
Direct answers on dosing, pharmacokinetics, side effects, and comparisons — cited where the answer is quantitative.
What is the semaglutide dosage for weight loss?
In the STEP 1 trial, the weight-management schedule reached a maintenance dose of 2.4 mg once weekly subcutaneously, climbing through 0.25, 0.5, 1.0, and 1.7 mg over the preceding weeks [1][15]. At that maintenance dose, mean body weight changed by -14.9% versus -2.4% with placebo at 68 weeks [1]. This is the documented trial schedule, not dosing advice for any individual.
How many mg is 40 units of semaglutide?
"Units" on a syringe measure volume, not milligrams, so the milligram amount depends entirely on the concentration of the specific preparation — there is no fixed conversion. Because dosing errors with non-standard preparations have been documented, especially with compounded products, the published literature emphasizes using approved, clearly labeled products [15]. No conversion is provided here; this is a research digest, not dosing guidance.
How long does semaglutide stay in your system?
Semaglutide has an elimination half-life of about one week (roughly 165-168 hours), so it clears slowly: effectively complete clearance takes about five weeks (around five half-lives) after the final dose [13][15]. This long persistence is why dosing is once weekly and why label guidance advises a multi-week interval before a planned pregnancy [15].
What is the half-life of semaglutide?
The elimination half-life of semaglutide is approximately one week — commonly cited as about 165-168 hours — for both the injectable and oral formulations [13][15]. A 2024 systematic review confirmed this long half-life as the basis for once-weekly subcutaneous dosing, alongside AUC, Cmax, and clearance parameters [13]. The chemistry behind it is albumin binding plus DPP-4 resistance.
Does semaglutide need to be refrigerated?
Per approved labeling, pre-filled pens are typically stored refrigerated (2-8 C) before first use and may then be kept at room temperature (at or below 30 C) for a defined in-use period, commonly cited as up to 56 days [15]. The oral tablet is supplied co-formulated with SNAC and is not reconstituted [23]. Storage should follow the specific product's labeling.
How long does compounded semaglutide last in the fridge?
Reconstituted research preparations are generally kept at 2-8 C and used within about 28 days [15], but compounded products vary by preparation and lack the standardized stability data of the approved product. The FDA documented quality and safety concerns with compounded semaglutide during the shortage [15]. Storage and beyond-use dating for any compounded preparation should follow that pharmacy's documentation, not a general figure.
What is semaglutide?
Semaglutide is a long-acting GLP-1 receptor agonist — a 31-amino-acid synthetic analogue of the gut hormone GLP-1, sharing about 94% of its sequence [15]. It is FDA-approved for type 2 diabetes, chronic weight management, cardiovascular risk reduction, and (2025) metabolic dysfunction-associated steatohepatitis, available as a once-weekly injection and a once-daily tablet [15].
What is semaglutide used for?
Semaglutide is used for type 2 diabetes, chronic weight management, reducing major adverse cardiovascular events in people with established cardiovascular disease and overweight or obesity, and, as of 2025, metabolic dysfunction-associated steatohepatitis [3][6][24]. In STEP 1 it produced a mean weight change of -14.9% at 68 weeks [1]; in SELECT it cut cardiovascular events by 20% [3].
How does semaglutide work?
Semaglutide activates GLP-1 receptors, which boosts glucose-dependent insulin secretion, suppresses glucagon, and slows gastric emptying [5][15]. Its weight effect is mainly central: in rodents it reaches brain appetite circuits (arcuate nucleus, area postrema, parabrachial nucleus), activating satiety neurons and inhibiting hunger neurons to reduce food intake without lowering energy expenditure [4].
How does semaglutide work for weight loss?
For weight loss, the dominant mechanism is appetite reduction via the brain. Rodent studies show semaglutide engages hypothalamic and brainstem circuits to cut food intake and shift food preference without reducing energy expenditure [4]. Clinically, this translated to a -14.9% mean body-weight change versus -2.4% for placebo at 68 weeks in STEP 1 [1].
What is compounded semaglutide?
Compounded semaglutide is semaglutide prepared by a compounding pharmacy rather than the approved manufactured product. It was permitted during a federally declared shortage (roughly 2022 to early 2025), during which the FDA documented dosing errors and products with unverified ingredients; the pathway was curtailed once the shortage resolved in 2025 [15]. It falls outside the approved-product evidence base.
What are the side effects of semaglutide?
The dominant side effects are gastrointestinal — nausea (in roughly one-third of patients), vomiting, diarrhea, and constipation — usually mild-to-moderate and concentrated during dose escalation [5][16]. Increased biliary (gallstone) disease is reported, and in SUSTAIN-6 diabetic-retinopathy complications were higher with rapid glycemic correction (HR 1.76) [2][5]. See the effects page for the full record.
How long does it take for semaglutide to work?
Glucose effects begin early, but the weight and full clinical effects build over months alongside the slow titration. STEP 1 measured its primary mean weight change of -14.9% at week 68 [1], and steady-state drug levels accumulate over several weeks because of the one-week half-life [13]. The trials report effects over a 68-72 week horizon, not days.
Is oral semaglutide as effective as the injection?
A meta-analysis of once-daily oral semaglutide reported efficacy in glycemic control and weight with class-consistent cardiovascular outcomes [11]. Both formulations share the same one-week half-life [13][15], but the oral tablet's bioavailability is only ~0.4-1% and depends on strict fasted dosing [23], making technique more consequential than with the injection. See the oral semaglutide page.
How long does it take for semaglutide to suppress appetite?
Appetite effects are central and can appear early, but they build as the dose climbs. Rodent work shows semaglutide rapidly engages brain appetite circuits to reduce food intake [4], and community reports describe quieter "food noise" within the first week or two (anecdotal). Clinically, the effect is sustained across the 68-week STEP 1 horizon [1].
Why am I not losing weight on semaglutide?
Response varies between individuals, and this site does not give personal advice — any concern about response belongs with a prescriber. For context, STEP 1 reported a mean change of -14.9%, an average around which individual results scatter [1], and a body-composition substudy noted that some of the weight lost is lean mass, motivating protein and resistance-training research [9]. Titration stage and adherence also matter.
Does semaglutide make you tired?
Fatigue is commonly reported by users, especially in the first day or two after each injection and during early weeks, usually easing with time (anecdotal, not a trial endpoint). A dedicated safety review frames the dominant adverse effects as gastrointestinal rather than fatigue [5]; tiredness reports are often linked by users to eating very little or under-hydration during titration.
Is semaglutide a GLP-1?
Yes. Semaglutide is a GLP-1 receptor agonist — a synthetic analogue of glucagon-like peptide-1 sharing about 94% of the native hormone's sequence, engineered with a DPP-4-resistant substitution and an albumin-binding side chain for a one-week half-life [15]. Its cardiovascular benefit in SUSTAIN-6 (HR 0.74) is a class-relevant outcome [2].
Does semaglutide cause hair loss?
A pharmacovigilance disproportionality analysis found a reporting signal for alopecia with semaglutide and tirzepatide [21], and a dermatology study linked telogen effluvium — reversible diffuse shedding — to the magnitude and rate of weight loss [22]. The signal is most consistent with rapid-weight-loss-associated shedding rather than a direct drug effect, and is generally described as temporary.
How fast does semaglutide work?
Pharmacologically, drug levels rise over several weeks to steady state because of the one-week half-life [13], so the schedule is built for months, not days. STEP 1 measured its primary weight outcome of -14.9% at 68 weeks [1]. Glucose-lowering can be seen earlier in diabetes trials, but the headline weight effect is a long-horizon result.
What is the difference between semaglutide and tirzepatide?
Tirzepatide is a dual GIP/GLP-1 receptor agonist; semaglutide is GLP-1-only. In the SURMOUNT-5 head-to-head trial (n=751) of adults with obesity, tirzepatide produced greater mean weight loss at 72 weeks (-20.2% vs -13.7%; P<0.001) [7]. Both are large effects; tirzepatide was larger in this direct comparison.
What is the downside of semaglutide?
The main downsides are gastrointestinal side effects during titration [5][16], substantial weight regain after stopping (a mean ~11.6 percentage points within a year in the STEP 1 extension) [19], loss of some lean mass [9], and, in diabetes, a retinopathy-worsening signal with rapid glycemic correction [2]. It is a chronic, not curative, therapy. See the effects page.