Q&A
Semaglutide questions, answered from the trial record
Direct answers to the most-asked semaglutide questions — each one tied to the study behind it.
What is the difference between semaglutide and tirzepatide?
Semaglutide activates one hormone receptor (GLP-1); tirzepatide activates two (GLP-1 and GIP). That difference shows up in results: in the SURMOUNT-5 head-to-head (n=751), tirzepatide produced greater weight loss at 72 weeks, -20.2% vs -13.7% (P<0.001) [1]. Semaglutide, however, has the deeper hard-endpoint outcome record.
Is tirzepatide better than semaglutide?
On weight loss, the direct trial favors tirzepatide: -20.2% vs -13.7% over 72 weeks in SURMOUNT-5 (P<0.001) [1], and it also led on HbA1c and weight in SURPASS-2 [9]. "Better" overall is not settled, though — semaglutide has the broader published outcome evidence, cutting cardiovascular events 20% in SELECT [3].
How much more weight do you lose on tirzepatide vs semaglutide?
In SURMOUNT-5, the direct head-to-head, the gap was about 6.5 percentage points: tirzepatide -20.2% versus semaglutide -13.7% at 72 weeks (P<0.001) [1]. For reference, semaglutide alone produced -14.9% versus -2.4% on placebo over 68 weeks in STEP 1 [2]. The exact gap depends on the population and trial.
What is semaglutide?
Semaglutide is a 31-amino-acid peptide engineered as a long-acting copy of the gut hormone GLP-1, sharing about 94% of its sequence [27]. It is FDA-approved for type 2 diabetes, chronic weight management, cardiovascular-risk reduction, and MASH. In STEP 1 it produced -14.9% mean weight loss over 68 weeks versus -2.4% on placebo [2].
What is semaglutide used for?
Semaglutide is FDA-approved for type 2 diabetes, chronic weight management, reducing major cardiovascular events in people with established cardiovascular disease, and (2025) the fatty-liver condition MASH. Its weight effect is large — -14.9% in STEP 1 over 68 weeks versus -2.4% on placebo [2] — and it also cut cardiovascular events 20% in SELECT [3].
How does semaglutide work?
Semaglutide switches on the GLP-1 receptor, boosting glucose-dependent insulin, suppressing glucagon, and slowing stomach emptying. Its weight effect is mainly central: rodent work showed it reaches the brainstem, area postrema and hypothalamic arcuate nucleus, reducing food intake and altering food preference without lowering energy expenditure [6] — it turns down hunger rather than speeding up calorie burn.
How does semaglutide work for weight loss?
By acting on appetite circuits in the brain. Preclinical work showed semaglutide lowers body weight through distributed central pathways — reduced food intake and altered food preference, with no fall in energy expenditure [6]. The clinical payoff: -14.9% mean body-weight change over 68 weeks in STEP 1 versus -2.4% on placebo [2].
What is the semaglutide dosage for weight loss?
In the STEP weight-management trials, the documented dose was once-weekly subcutaneous semaglutide titrated from 0.25 mg up to a 2.4 mg maintenance dose, which produced -14.9% mean weight loss over 68 weeks versus -2.4% on placebo [2]. This is the trial regimen, stated as a study fact — not a recommendation for any individual.
How many mg is 40 units of semaglutide?
This digest does not convert "units" to milligrams, because that depends entirely on a specific product's concentration and risks being read as dosing guidance. Semaglutide carries a low drug-drug-interaction risk despite delayed gastric emptying [16], but any dose or unit question for an individual is a clinical matter — and there is no clinician here.
What is compounded semaglutide?
Compounded semaglutide is prepared by a compounding pharmacy rather than supplied as the approved manufactured product; it was permitted during the 2022-2025 shortage and curtailed once that was declared resolved. The entire trial record — including SUSTAIN-6's 26% cut in cardiovascular events [4] — was generated with the approved product, not compounded versions, which carry documented quality concerns.
What are the side effects of semaglutide?
Gastrointestinal effects dominate: nausea (roughly one-third of patients), vomiting, diarrhea and constipation, mostly mild-to-moderate and concentrated during dose escalation [7]. Other cautions include a boxed thyroid warning and, in SUSTAIN-6, more diabetic-retinopathy complications with rapid glycemic correction (HR 1.76) [4]. The full cited list is on the effects page.
How long does it take for semaglutide to work?
Appetite effects often appear within the first weeks, but the trial endpoints are measured over months. STEP 1 reported its -14.9% mean weight loss across 68 weeks of treatment [2]; doses are deliberately stepped up slowly to limit nausea, so the full effect builds gradually rather than arriving at once.
How long does semaglutide stay in your system?
Semaglutide's elimination half-life is approximately one week (~165-168 hours), so it is effectively cleared about five weeks after the last dose [27]. That long half-life — from albumin binding plus DPP-4 resistance — is also why its drug-interaction risk stays low despite delayed gastric emptying [16].
What is the half-life of semaglutide?
Approximately one week — commonly cited as ~165-168 hours — for both the subcutaneous and oral forms, with effectively complete clearance roughly five weeks after the final dose [27]. The long half-life comes from strong reversible albumin binding via the fatty-acid side chain and DPP-4 resistance from the Aib-8 substitution.
Is oral semaglutide as effective as the injection?
It depends on dose and on correct administration. A meta-analysis of once-daily oral semaglutide reported efficacy in glycemic control and weight, with cardiovascular outcomes consistent with the GLP-1 class [11]. But oral bioavailability is only ~0.4-1% even with the SNAC enhancer, so strict fasted dosing matters [17]; higher oral doses (25-50 mg) were studied to push efficacy further [14].
How long does it take for semaglutide to suppress appetite?
Appetite suppression is the effect people report earliest, often within the first week or two, consistent with semaglutide's central mechanism — it reaches brainstem and hypothalamic appetite circuits to reduce food intake [6]. The measurable weight change, though, accrues over months as the dose is titrated up, reaching -14.9% by week 68 in STEP 1 [2].
Why am I not losing weight on semaglutide?
This digest can't assess any individual, but the trial context helps: STEP 1's -14.9% was a mean, so responses varied around it [2], and the dose is titrated slowly from 0.25 mg toward 2.4 mg, so early on the full dose hasn't been reached [2]. Plateaus also appear as loss naturally slows after the early period. Any personal troubleshooting is a clinical question.
Does semaglutide make you tired?
Fatigue is commonly reported anecdotally, especially in the first day or two after an injection and during early weeks, usually easing with time (see the effects page). In trials, the dominant adverse effects are gastrointestinal rather than fatigue [7]; semaglutide's headline outcome data, meanwhile, include a 26% cut in cardiovascular events in SUSTAIN-6 (HR 0.74) [4].
Is semaglutide a GLP-1?
Yes — semaglutide is a GLP-1 receptor agonist, a long-acting copy of the natural incretin hormone GLP-1 that activates the GLP-1 receptor [27]. That class membership underlies both its benefits and its class warnings; in SUSTAIN-6 it cut major cardiovascular events 26% (HR 0.74; 95% CI 0.58-0.95) in type 2 diabetes at high risk [4].
Does semaglutide cause hair loss?
Hair loss appears as a pharmacovigilance signal, not a confirmed drug effect. A disproportionality analysis flagged alopecia with semaglutide and tirzepatide [25], and a dermatology study linked telogen effluvium — reversible diffuse shedding — to the rate and magnitude of weight loss [26]. The signal is most consistent with rapid-weight-loss-driven shedding, which is typically temporary.
How fast does semaglutide work?
Appetite changes are often felt within the first weeks, but trial weight endpoints build over months because the dose is stepped up slowly to limit nausea. STEP 1 measured its -14.9% mean weight loss over 68 weeks of treatment versus -2.4% on placebo [2]; there is no documented overnight effect.
What is the downside of semaglutide?
The main downsides: gastrointestinal intolerance during titration (nausea, vomiting, diarrhea, constipation) that drives most discontinuations [7]; weight regain after stopping (mean ~11.6 points within a year in the STEP 1 extension) [23]; and class warnings including thyroid (boxed) and pancreatitis. SUSTAIN-6 also found more retinopathy complications with rapid glycemic correction (HR 1.76) [4].