QUESTIONS
Semaglutide, answered: the questions people actually ask.
Short, direct, cited answers — starting with the tirzepatide comparison and working through dosing, effects and timing.
What is the difference between semaglutide and tirzepatide?
Semaglutide targets one gut-hormone receptor (GLP-1); tirzepatide is a dual agonist that targets two (GIP and GLP-1). In the SURMOUNT-5 head-to-head (n=751) in adults with obesity, tirzepatide produced greater mean weight loss at 72 weeks — -20.2% versus -13.7% for semaglutide (P<0.001) [7]. Semaglutide, though, carries the larger cardiovascular- and kidney-outcomes evidence base [3][6].
Is tirzepatide better than semaglutide?
For weight loss specifically, the one direct head-to-head trial favors tirzepatide: -20.2% versus -13.7% in SURMOUNT-5 over 72 weeks (P<0.001) [7]. "Better" depends on the goal, though — semaglutide has the larger documented cardiovascular-outcomes trial (SELECT, -20% MACE) [3] and a kidney-outcomes trial (FLOW, -24%) [6], and it comes as both a pill and a shot. There is no single winner across every endpoint.
How much more weight do you lose on tirzepatide vs semaglutide?
In the SURMOUNT-5 head-to-head, the gap was about 6.5 percentage points: tirzepatide -20.2% versus semaglutide -13.7% at 72 weeks (P<0.001) [7]. For context on semaglutide's own number, STEP 1 found a mean -14.9% versus -2.4% with placebo at week 68 [1]. Averages differ from individual results, and tolerability shapes real-world outcomes.
What is semaglutide?
Semaglutide is an FDA-approved GLP-1 receptor agonist — a long-acting copy of the gut hormone GLP-1, engineered to last about a week in the body [11]. In STEP 1, once-weekly subcutaneous 2.4 mg produced a mean body-weight change of -14.9% versus -2.4% with placebo at week 68 in adults with overweight or obesity without diabetes [1]. It is approved for diabetes, weight management, cardiovascular risk reduction, and (2025) a fatty-liver disease.
What is semaglutide used for?
Semaglutide is FDA-approved for type 2 diabetes, chronic weight management, reducing major adverse cardiovascular events in people with established cardiovascular disease, and (since 2025) metabolic dysfunction-associated steatohepatitis (MASH) [12]. Its weight evidence comes from STEP 1 (-14.9% at week 68) [1] and its cardiovascular evidence from SELECT (-20% MACE) [3].
How does semaglutide work?
Semaglutide activates the GLP-1 receptor. Rodent work showed it reaching the brainstem and hypothalamic arcuate nucleus — the appetite-control hubs — to reduce food intake and shift food preference without lowering energy expenditure [4]. It also boosts glucose-dependent insulin, lowers glucagon, and slows gastric emptying [5]. In short: it turns down hunger and steadies blood sugar.
How does semaglutide work for weight loss?
The weight effect is mostly central, not metabolic. Semaglutide reaches the brain's appetite circuits and quiets hunger while boosting fullness, so people eat less without their calorie burn dropping [4]. In STEP 1, that produced a mean body-weight change of -14.9% versus -2.4% with placebo at week 68 [1]. People describe it as the constant "food noise" going quiet.
What is the semaglutide dosage for weight loss?
In STEP 1, the studied weight-management regimen was once-weekly subcutaneous semaglutide titrated to a 2.4 mg maintenance dose, which produced a mean -14.9% body-weight change versus -2.4% with placebo at week 68 [1]. The documented ladder climbs from 0.25 mg over about 16 weeks. This is the trial-documented schedule, reported in the third person — not a dose for any individual to follow.
How many mg is 40 units of semaglutide?
This site does not provide unit-to-milligram conversions, because such math is exactly the kind of individualized dosing instruction that belongs with a prescriber and a specific product. What the literature documents are studied doses — for example, a 2.4 mg once-weekly maintenance dose for weight management — summarized as research figures, not as a personal calculation [10]. For any conversion, consult a clinician and the specific product labeling.
What is compounded semaglutide?
Compounded semaglutide is the drug prepared by a compounding pharmacy rather than the approved manufactured product. It was permitted during a federally declared shortage from roughly 2022 into early 2025; once the shortage was declared resolved, the compounding pathways were curtailed [12]. The approved-product trial evidence summarized here does not extend to compounded or non-pharmaceutical sources.
What are the side effects of semaglutide?
The dominant side effects are gastrointestinal — nausea (about one-third of patients), vomiting, diarrhea and constipation — mostly mild-to-moderate and concentrated during dose escalation [13][5]. Documented cautions include increased gallstone risk [5], worsening of pre-existing diabetic retinopathy with rapid glucose correction (SUSTAIN-6) [2], and class warnings for thyroid C-cell tumors and pancreatitis [14]. See Semaglutide effects for the full, cited picture.
How long does it take for semaglutide to work?
Appetite effects often begin within the first weeks, but the trial-level weight result is measured over many months: STEP 1 reported its -14.9% mean change at week 68 [1]. Because the dose is titrated upward over roughly the first four months, the full effect builds gradually rather than arriving at once. Individual timing varies.
How long does semaglutide stay in your system?
Semaglutide's elimination half-life is approximately one week, so it remains in circulation for roughly five weeks after the last dose [11]. That long persistence comes from its tight, reversible binding to the blood protein albumin plus resistance to the enzyme DPP-4. It is also why a multi-week washout is advised before a planned pregnancy.
What is the half-life of semaglutide?
The elimination half-life of semaglutide is approximately one week (commonly cited as ~165-168 hours) for both the subcutaneous and oral forms, with effectively complete clearance about five weeks after the final dose [11]. This long half-life is the structural basis for once-weekly subcutaneous dosing.
Is oral semaglutide as effective as the injection?
The two forms are studied in different programs rather than a single head-to-head, so a clean equivalence cannot be claimed here. Oral semaglutide (PIONEER, OASIS) showed dose-dependent glycemic and weight benefits [10], but its bioavailability is low (~0.4-1%) and requires strict fasted dosing, so administration errors can reduce the absorbed dose [20]. The injection is the route used in the large outcome trials (SELECT, FLOW) [3][6].
How long does it take for semaglutide to suppress appetite?
Appetite suppression is often noticed early — within the first week or two in patient reports — consistent with the drug's rapid central action on appetite circuits [4]. Because the dose is escalated over the first months, the effect typically deepens as the dose rises. This is reported, not promised: timing and intensity vary by person.
Why am I not losing weight on semaglutide?
This site does not give individual treatment guidance, so it cannot diagnose any one person's response. What the trials show is that the average weight change in STEP 1 was -14.9% at week 68, but that is a mean — responses spread around it, and the dose is titrated gradually [1]. Questions about an individual response belong with a clinician who knows the full picture.
Does semaglutide make you tired?
Tiredness is commonly reported in patient communities, especially in the day or two after each injection and during the early weeks, usually easing with time — anecdotal, not a controlled-trial finding. In the trial record, the adverse-effect profile is dominated by gastrointestinal events rather than fatigue [5]. Some report that staying hydrated and eating enough helps. See the effects page.
Is semaglutide a GLP-1?
Yes. Semaglutide is a GLP-1 receptor agonist — a synthetic analogue of the incretin hormone GLP-1 (glucagon-like peptide-1) that activates the GLP-1 receptor [11]. Its safety and efficacy as a GLP-1 receptor agonist are documented across the SUSTAIN, STEP, SELECT and FLOW programs [3][6]. Tirzepatide, by contrast, targets two receptors (GIP and GLP-1).
Does semaglutide cause hair loss?
Hair shedding appears as a pharmacovigilance reporting signal for semaglutide and tirzepatide [18], but the leading explanation is telogen effluvium — a reversible, diffuse shedding triggered by rapid weight loss — rather than direct drug toxicity [19]. It is most often noticed a few months in and described as temporary. It is a real but secondary signal, not a confirmed direct effect.
How fast does semaglutide work?
Appetite effects tend to appear within the first weeks, but the headline weight outcome is a months-long measure — STEP 1 reported -14.9% at week 68 [1]. Because dosing is escalated slowly to limit nausea, the effect accumulates over the first several months rather than arriving immediately. Individual pace varies.
What is the downside of semaglutide?
The main downsides: gastrointestinal side effects (nausea in about a third of patients, plus vomiting, diarrhea, constipation), concentrated during titration [13][5]; substantial weight regain after stopping (a mean ~11.6 percentage points within a year) [17]; loss of some lean mass alongside fat [16]; and class warnings (thyroid C-cell tumors, pancreatitis) carried without a confirmed human signal [14]. Tirzepatide also outperformed it on head-to-head weight loss [7].