Semaglutide FAQ: Oral vs Injectable, Doses, Side Effects and More
What is compounded semaglutide?
Compounded semaglutide is semaglutide made by a compounding pharmacy rather than the approved manufactured product. It was permitted during a federally declared shortage (about 2022 to early 2025), but the FDA documented dosing errors, hospitalizations, and products with unverified or non-pharmaceutical ingredients; the pathway was curtailed once the shortage was declared resolved in 2025 [5]. It sits outside the trial evidence base.
Is oral semaglutide as effective as the injection?
Both forms work, but they differ in absorption. Oral semaglutide is co-formulated with the absorption enhancer SNAC and has only ~0.4-1% bioavailability, so it needs strict empty-stomach dosing and much higher milligram doses [8]. At 50 mg once daily it produced meaningful weight loss in the OASIS program [9], while the once-weekly injection (~89% absorbed) anchors the big outcome trials [1].
How do you inject semaglutide and where?
The injectable form is given under the skin (subcutaneous) once weekly — typically the abdomen, thigh, or upper arm — as documented in the trial protocols and labeling [1][2]. Trials titrated the dose upward gradually to ease tolerability. This describes how the studies administered it in the third person; it is not personal instruction. Some people report milder side effects when rotating the injection area.
How do you microdose semaglutide?
There is no established "microdosing" protocol in the approved evidence base. The trials used defined escalation schedules — for the injection, starting at 0.25 mg once weekly and stepping up over about four months to a target such as 2.4 mg [1]. The very low oral bioavailability (~0.4-1%) also makes sub-label oral dosing unpredictable [8]. We report studied doses only, not how to take less.
What is semaglutide?
Semaglutide is a GLP-1 receptor agonist — a long-acting, lab-made copy of the gut hormone GLP-1 — available as a once-daily tablet and a once-weekly injection. It's a 31-amino-acid peptide engineered to resist the DPP-4 enzyme and bind albumin, giving it a roughly one-week half-life [5]. It's FDA-approved for type 2 diabetes, chronic weight management, cardiovascular risk reduction, and (2025) liver disease (MASH).
What is semaglutide used for?
Semaglutide is approved for type 2 diabetes, chronic weight management, reducing major cardiovascular events in people with established cardiovascular disease, and, as of 2025, metabolic dysfunction-associated steatohepatitis (MASH). Its weight effect is large — a mean -14.9% at 68 weeks in STEP 1 [1] — and its cardiovascular benefit reached a 20% reduction in major events in SELECT [3].
How does semaglutide work?
It switches on GLP-1 receptors in the pancreas (boosting insulin only when blood sugar is high and quieting glucagon), in the gut (slowing stomach emptying), and in the brain's appetite centers. A rodent study showed it reaches the brainstem and hypothalamus to switch on satiety neurons and switch off hunger neurons, cutting food intake without lowering calories burned [4].
How does semaglutide work for weight loss?
The weight effect is mostly central. Semaglutide reaches appetite circuits in the brain — the arcuate nucleus and brainstem area postrema — turning up satiety-promoting POMC/CART neurons and turning down hunger-driving NPY/AgRP neurons, which reduces how much people eat [4][13]. In STEP 1, that translated to a mean -14.9% body weight at 68 weeks versus -2.4% on placebo [1].
What is the semaglutide dosage for weight loss?
In STEP 1, the injectable weight-management dose was 2.4 mg once weekly, reached by stepping up from 0.25 mg over about four months; it produced a mean -14.9% body-weight change at 68 weeks [1]. The oral OASIS program studied 50 mg once daily [9]. These are trial-documented doses reported in the third person, not a recommendation for any individual.
How many mg is 40 units of semaglutide?
"Units" usually refers to insulin-syringe markings, not an official semaglutide measure, so unit-to-mg conversions depend entirely on a product's specific concentration and are a common source of dosing error. The trials and labeling specify doses in milligrams (for the injection, up to 2.4 mg weekly) [1]. Because mismeasurement risk is real — and prominent with compounded products — we report only the milligram doses the studies used [5].
What are the side effects of semaglutide?
The dominant side effects are gastrointestinal — nausea (in roughly a third of patients), vomiting, diarrhea, and constipation — mostly mild-to-moderate and concentrated during dose increases [5]. Other cited cautions include gallstones, a boxed thyroid-tumor warning (rodent-derived, human-unconfirmed), worsening of pre-existing diabetic retinopathy with rapid glucose correction (HR 1.76 in SUSTAIN-6), and lean-mass loss [2][5].
How long does it take for semaglutide to work?
Because the half-life is about a week, it takes several weeks of dosing to reach steady levels, and trials titrated the dose over roughly four months [1][5]. Appetite and early weight effects often appear within the first weeks, but the large STEP 1 average of -14.9% was measured at 68 weeks [1]. Blood-sugar effects in diabetes trials were assessed over months.
How long does semaglutide stay in your system?
Semaglutide's elimination half-life is about one week (~165-168 hours), so it clears slowly — effectively complete clearance takes roughly five weeks after the last dose [5]. This long tail is driven by strong, reversible albumin binding plus DPP-4 resistance, and it's the same for the tablet and the injection [5][8].
What is the half-life of semaglutide?
About one week — commonly cited as ~165-168 hours — for both the oral and subcutaneous forms [5]. Half-life is the time for blood levels to fall by half; a one-week value is what allows once-weekly injection. It comes from the C18 fatty-acid side chain binding albumin and the Aib substitution blocking DPP-4 [5].
How long does it take for semaglutide to suppress appetite?
Many people report reduced appetite and quieter "food noise" within the first week or two (anecdotal, not a clinical endpoint). Mechanistically, semaglutide acts on brain appetite circuits — the arcuate nucleus and area postrema — to reduce food intake [4]. Because the half-life is ~1 week, full steady levels build over several weeks of dosing [5].
Why am I not losing weight on semaglutide?
Response varies between people, and trials report a range around the average. STEP 1's mean was -14.9% at 68 weeks, but that's an average — some lost much more and some much less [1]. Weight loss is also largely treatment-dependent (it regains after stopping) [1]. We summarize the trial averages; we can't and don't give individual medical advice on an individual's results.
Does semaglutide make you tired?
Fatigue is commonly reported, especially in the first day or two after an injection and during the early weeks, usually easing with time (this is anecdotal community reporting, not a controlled-trial endpoint). The dominant trial-documented adverse effects are gastrointestinal rather than fatigue [5]. Some people link early tiredness to eating very little or not drinking enough water.
Is semaglutide a GLP-1?
Yes. Semaglutide is a GLP-1 receptor agonist — a long-acting analogue of the natural incretin hormone GLP-1, sharing about 94% of its sequence and binding the same receptor [5]. Engineering edits (an Aib substitution and an albumin-binding fatty-acid tail) give it a ~1-week half-life versus GLP-1's roughly two minutes [5].
Does semaglutide cause hair loss?
A pharmacovigilance analysis flagged a hair-loss (alopecia) reporting signal, and a separate study linked telogen effluvium — a reversible, diffuse shedding — to the size and speed of weight loss [5]. The signal is most consistent with rapid-weight-loss shedding rather than a direct drug effect, and it's generally described as temporary.
How fast does semaglutide work?
Appetite changes are often noticed within the first weeks (anecdotally), but the measured weight effect builds over months — STEP 1's mean -14.9% was at 68 weeks [1]. Because the half-life is ~1 week, steady drug levels take several weeks to establish, and trials escalated the dose over roughly four months [1][5].
What is the difference between semaglutide and tirzepatide?
They're different molecules. Tirzepatide is a dual agonist (it activates a second gut-hormone receptor, GIP, alongside GLP-1), while semaglutide acts on GLP-1 alone. In the head-to-head SURMOUNT-5 trial (n=751), tirzepatide produced greater mean weight loss at 72 weeks (-20.2% vs -13.7%; P<0.001) [7]. Both results are large by historical standards.
What is the downside of semaglutide?
The main downsides: frequent gastrointestinal effects (nausea, vomiting, diarrhea, constipation), especially during dose increases [5]; substantial weight regain after stopping (~11.6 percentage points within a year in the STEP 1 extension) [1]; loss of some lean mass [5]; and class cautions including pancreatitis and a rodent-derived thyroid-tumor boxed warning [5]. SURMOUNT-5 also showed less weight loss than tirzepatide head-to-head [7].