Semaglutide

Semaglutide is a GLP-1(7-37) analogue with an Aib substitution at position 8 to resist DPP-4 cleavage and a C18 fatty-diacid chain that binds albumin, giving it a one-week half-life. At the pancreatic beta cell it potentiates glucose-dependent insulin secretion and suppresses glucagon; at the stomach it markedly slows emptying; in the arcuate nucleus and area postrema it drives satiety and reduces food reward. The cardiovascular benefit seen in SELECT and SUSTAIN-6 appears to go beyond weight and glucose, likely involving direct anti-inflammatory and endothelial effects. All of this is established in phase 3 outcome trials, not extrapolated.

Targets: GLP-1 receptor

• · 250 mcg weekly for 4 weeks, then 500, then 1000, then 1700, then 2400 mcg, each step held 4 weeks. Do not skip steps to chase results - nausea and vomiting scale directly with how fast you climb.
• · 250 mcg for 4 weeks, then 500 mcg, with 1000 and 2000 mcg available if glycaemic control needs it.
• · Rybelsus (diabetes) runs 3, 7 then 14 mg daily. The oral Wegovy pill approved in December 2025 is a separate product with its own strengths - 1.5, 4, 9 then 25 mg daily - and gave about 16.6% weight loss at 25 mg in OASIS 4. Do not start the weight-management product at a Rybelsus dose.

Work out your exact syringe units →

• very commonNausea— Worst in the 48 hours after a dose step; usually settles within 2-4 weeks at a stable dose.
• very commonConstipation or diarrhoea— Fibre, hydration and magnesium help; low food volume is often the real cause.
• very commonLoss of lean mass— Roughly 25-40% of total weight lost is lean tissue without resistance training and 1.6 g/kg protein.
• commonVomiting— Strongly dose-escalation-dependent.
• commonHair shedding— Telogen effluvium from rapid weight loss rather than a direct drug effect.
• uncommonGallstones and cholecystitis— Driven by rapid weight loss and reduced gallbladder motility.
• uncommonDelayed gastric emptying and aspiration risk under anaesthesia— Tell any anaesthetist. Most centres now want the drug held for a week before elective surgery.
• rarePancreatitis— Severe persistent abdominal pain radiating to the back means stop and get imaging.
• rareNon-arteritic anterior ischaemic optic neuropathy (sudden painless vision loss in one eye)— Added to EU product information as a very rare side effect in June 2025 after an EMA safety review. Sudden vision loss or a visual field defect in one eye means stop the drug and get same-day ophthalmology assessment - the damage is usually permanent.

• Personal or family history of medullary thyroid carcinoma or MEN2 - rodent C-cell tumours drove a boxed warning.
• History of pancreatitis.
• Pregnancy and breastfeeding - stop at least two months before trying to conceive.
• Severe gastroparesis or established diabetic gastroparesis.
• Active or recent proliferative diabetic retinopathy - rapid glucose correction worsened retinopathy in SUSTAIN-6.

• cautioninsulin-analogues — Real hypoglycaemia risk; mealtime insulin usually needs a 20-50% cut when semaglutide is added.
• cautionsulfonylureas (glimepiride, gliclazide, glipizide) — Real hypoglycaemia risk - unlike semaglutide alone, sulfonylureas drive insulin release independently of glucose. Labels advise reducing the sulfonylurea dose when a GLP-1 agonist is started.
• redundanttirzepatide — Same appetite axis. Running both stacks side effects without adding meaningful weight loss.
• synergycagrilintide — The basis of CagriSema - amylin adds satiety through a separate receptor and spares lean mass.
• redundantretatrutide — Retatrutide already contains full GLP-1 agonism.

• · Weight and waist circumference weekly, at the same time of day.
• · HbA1c every 3-6 months if diabetic or prediabetic.
• · DEXA or at minimum bioimpedance every 3-4 months to catch lean-mass loss early.
• · Lipase and amylase only if abdominal pain appears - routine screening is not useful.
• · Resting heart rate; a persistent 5-10 bpm rise is expected but more warrants a look.

FDA- and EMA-approved as Ozempic, Wegovy and Rybelsus. Compounded and grey-market 'research' semaglutide is widely sold and is not legally supplied for human use; FDA ended the shortage-based compounding allowance in 2025.

• Wilding et al. 2021, STEP 1, NEJM - 14.9% weight loss at 68 weeks (trial)
• Lincoff et al. 2023, SELECT, NEJM - 20% reduction in MACE in non-diabetic obesity (trial)
• Marso et al. 2016, SUSTAIN-6, NEJM (trial)
• Ozempic and Wegovy US prescribing information (label)

The GLP-1 receptor is a class B1 GPCR that couples primarily to Gs. Semaglutide binding raises intracellular cAMP, which activates both PKA and Epac2. In the beta cell that pair closes ATP-sensitive potassium channels and mobilises intracellular calcium, but only when glucose is already driving ATP production - that glucose dependence is the entire reason semaglutide does not cause hypoglycaemia on its own, and it is also why adding a sulfonylurea removes the safety net. Beta-arrestin recruitment matters too: semaglutide is comparatively cAMP-biased and recruits beta-arrestin less than native GLP-1, which slows receptor internalisation and keeps signalling going for days rather than minutes. The central effects run through two anatomically distinct routes. Direct GLP-1 receptors in the area postrema and nucleus tractus solitarius sit outside the blood-brain barrier and are reachable by circulating drug - this is the nausea and emesis pathway. Deeper hypothalamic effects on arcuate POMC/CART neurons appear to be reached both by limited direct penetration through circumventricular organs and indirectly by vagal afferent signalling. That two-route structure explains a clinical observation people find confusing: nausea habituates within weeks because area postrema signalling desensitises, while appetite suppression persists because the hypothalamic arm does not. Gastric emptying delay follows the same pattern - it is profound at first and partially tachyphylaxes with chronic long-acting exposure, which is why short-acting lixisenatide beats semaglutide on postprandial glucose despite being a far weaker drug overall. The SELECT cardiovascular benefit emerged early, before much weight had been lost, and tracked with reductions in CRP; the working explanation is direct anti-inflammatory and endothelial signalling rather than weight or glucose alone, but that remains an inference from the trial rather than a demonstrated mechanism.

Four failure modes account for most of it. First, escalating on the calendar rather than on tolerance - the label schedule is a maximum speed, not a target, and people who force the 1.7 to 2.4 mg step while still vomiting usually abandon the drug entirely. Second, losing 30-40% of total weight as lean tissue because nobody lifted anything or ate enough protein, which leaves someone lighter, weaker and with a lower resting metabolic rate than when they started - that is the setup for the regain everyone talks about. Third, dehydration. Several days of vomiting plus an ACE inhibitor plus a diuretic plus ibuprofen is a genuine recipe for acute kidney injury, and it is the most common reason GLP-1 users end up in hospital. Fourth, anaesthesia. Delayed gastric emptying means a stomach that is not empty after a standard fast, and aspiration under sedation is the serious version of this problem - tell the anaesthetist, and expect most centres to want a week's hold before an elective procedure. Two lesser problems: sulfur-tasting eructation and severe constipation are underrated quality-of-life killers that respond to magnesium citrate and actual fibre; and the June 2025 EMA addition of non-arteritic anterior ischaemic optic neuropathy means sudden painless loss of vision in one eye is a same-day ophthalmology problem, not something to watch.

1. 250 mcgWeeks 1-4 — Nausea here is normal and usually settles in 5-10 days. If it does not, you have learned something useful about your ceiling.
2. 500 mcgWeeks 5-8 — The first step that produces obvious appetite suppression for most people.
3. 1 mgWeeks 9-12 — Ozempic's usual maintenance dose for diabetes. Plenty of people get their full weight-loss result here and never need to go higher.
4. 1.7 mgWeeks 13-16 — Common stopping point for tolerability. Holding here for 8-12 weeks before deciding is smarter than pushing on schedule.
5. 2.4 mgWeek 17 onward — The STEP 1 dose that produced 14.9% mean weight loss. Not a target everyone needs to reach.

• GLP-1 receptor (GLP1R), class B1 GPCR — Low-nanomolar; the commonly quoted figure is a Ki around 0.38 nM from the original Novo Nordisk discovery paper, which was not re-verified in this session

  Full Gs-coupled agonism. Glucose-dependent insulin secretion, glucagon suppression, delayed gastric emptying, central satiety, reduced food reward, and a 3-5 bpm rise in resting heart rate through sinoatrial GLP-1 receptors.

• Albumin (not a receptor, but functionally the drug's depot) — Greater than 99% bound

  Reversible binding of the C18 di-acid to fatty-acid binding sites on serum albumin. This is what converts a 2-minute hormone into a 7-day drug, and it is why free-fraction changes in hypoalbuminaemia are worth thinking about even though no dose adjustment is recommended.

• STEP 1 Phase 3 · n=1961 · 68 weeks · 2021

  Mean weight change of -14.9% with semaglutide 2.4 mg weekly versus -2.4% with placebo.

• SELECT Phase 3 cardiovascular outcomes · n=17604 · 208 weeks · 2023

  20% relative reduction in major adverse cardiovascular events in people with overweight or obesity and established cardiovascular disease but without diabetes.

• SUSTAIN-6 Phase 3 cardiovascular outcomes · n=3297 · 104 weeks · 2016

  26% reduction in the composite cardiovascular endpoint in type 2 diabetes, with a signal of worsened diabetic retinopathy attributed to rapid glucose correction.

• OASIS 1 Phase 3 · n=667 · 68 weeks · 2023

  Oral semaglutide 50 mg once daily produced weight loss comparable to the 2.4 mg weekly injection in adults with overweight or obesity.

• OASIS 2 Phase 3 · 68 weeks · 2025

  Oral semaglutide 50 mg in an East Asian population with overweight or obesity, with and without type 2 diabetes.

• SURMOUNT-5 Phase 3 head-to-head · n=751 · 72 weeks · 2025

  Semaglutide 2.4 mg lost 13.7% versus 20.2% for tirzepatide - the cleanest direct comparison available and a loss for semaglutide.

Days 1-7: appetite suppression is usually unmistakable within 48-72 hours of the first injection, along with the first nausea. Weeks 2-4: food volume drops, early weight loss is substantially water and gut content, and constipation appears. Weeks 4-5: steady state is reached, which is the point at which what you are feeling is the real drug level rather than a rising one. Weeks 8-16: fat loss becomes the dominant component and the alcohol and general reward-seeking effects that people report often become noticeable here. Weeks 20-40: the steepest phase of the weight curve. Weeks 60-70: plateau in STEP 1. Stopping: appetite returns within two to three weeks, and roughly two-thirds of lost weight comes back within a year without a deliberate maintenance plan.

The only combination with real trial evidence behind it is cagrilintide, and that exists as a finished product (CagriSema) rather than something you should be mixing yourself. Everything else worth doing alongside semaglutide is not a peptide. Resistance training three times a week and 1.6-2.2 g/kg of protein is the intervention that changes body composition outcomes, and no amount of peptide stacking substitutes for it. Creatine monohydrate at 5 g daily is cheap and helps hold onto strength during a large deficit. If you are running a growth-hormone secretagogue for other reasons, be aware ghrelin-receptor agonists like ipamorelin and MK-677 push appetite in the opposite direction and MK-677 also worsens fasting glucose, so you are paying twice. Adding tirzepatide or retatrutide on top is not a stack, it is the same receptor twice - you get additive nausea and no additive weight loss. The genuinely useful adjuncts are boring: magnesium and fibre for constipation, ondansetron if nausea is limiting escalation, and a proton pump inhibitor if reflux from delayed emptying becomes the limiting factor.

Against tirzepatide: SURMOUNT-5 is the only head-to-head and semaglutide lost, 13.7% versus 20.2%. Semaglutide's counter-arguments are the SELECT cardiovascular outcome data in people without diabetes, a longer real-world safety record, and an oral option. Against liraglutide: same receptor, roughly double the effect, one injection a week instead of seven. Against dulaglutide: dulaglutide is the better-tolerated diabetes drug and a much weaker weight drug, because a 60 kDa Fc-fusion does not reach central GLP-1 receptors the way a small acylated peptide does. Against CagriSema: REDEFINE-1 gave 20.4% versus semaglutide's 15%, but REDEFINE-4 failed to beat tirzepatide, so CagriSema is best understood as semaglutide's replacement rather than a leap. Against orforglipron: the pill is real and gives roughly 11-12%, which is meaningfully less - the pill is a convenience and supply argument, not an efficacy one.

$200–$1350/month. Wide range because the market is fragmented. Manufacturer cash-pay programmes and telehealth sit around 200-500 per month; full US list price for Wegovy or Ozempic without insurance is roughly 1,000-1,350. Compounded and grey-market vials undercut all of that at 50-150 per month, with the corresponding uncertainty about what is actually in them. These are market observations from mid-2026, not verified prices.

• ?The GLP-1 receptor binding affinity figure (Ki around 0.38 nM) is widely quoted but was not independently resolved in this session.
• ?The amino-acid sequence given is the standard published sequence and matches the label's description of the position 8, 26 and 34 modifications, but the residue-by-residue string was not verified against a primary structural source, so it carries verified:false.
• ?Whether the SELECT cardiovascular benefit is independent of weight loss remains an inference from timing and CRP data, not a demonstrated mechanism.
• ?The proportion of weight lost as lean mass varies enormously between studies (roughly 25-40%) and depends heavily on baseline body composition, protein intake and training - single-number claims about it should be distrusted.
• ?Long-term (beyond about five years) outcomes on bone density, muscle function in older users and pregnancy exposure are not characterised.
• ?The mechanism behind the NAION signal is unknown and the absolute risk has not been well quantified.
• ?Cost figures are market observations, not verified pricing.

• Once-Weekly Semaglutide in Adults with Overweight or Obesity Wilding JPH et al., N Engl J Med, 2021 · PMID 33567185

  STEP 1. The trial that defined what 2.4 mg weekly does over 68 weeks.

• Semaglutide and Cardiovascular Outcomes in Obesity without Diabetes Lincoff AM et al., N Engl J Med, 2023 · PMID 37952131

  SELECT. The reason semaglutide is a cardiovascular drug and not only a weight drug.

• Semaglutide and Cardiovascular Outcomes in Patients with Type 2 Diabetes Marso SP et al., N Engl J Med, 2016 · PMID 27633186

  SUSTAIN-6, including the retinopathy signal that still shapes how fast you should correct a very high HbA1c.

• Efficacy and safety of semaglutide compared with liraglutide and placebo for weight loss in patients with obesity: a randomised, double-blind, placebo and active controlled, dose-ranging, phase 2 trial O'Neil PM et al., Lancet, 2018 · PMID 30122305

  The dose-ranging study that picked 2.4 mg and showed where the dose-response curve flattens.

• Oral semaglutide 50 mg taken once per day in adults with overweight or obesity (OASIS 1): a randomised, double-blind, placebo-controlled, phase 3 trial Knop FK et al., Lancet, 2023 · PMID 37385278

  The oral weight-management data.

• Oral Semaglutide in an East Asian Population With Overweight or Obesity, With or Without Type 2 Diabetes: The OASIS 2 Randomized Clinical Trial Kadowaki T et al., JAMA Intern Med, 2025 · PMID 40758358

  Oral semaglutide outside a predominantly Western population.

• Tirzepatide as Compared with Semaglutide for the Treatment of Obesity Aronne LJ et al., N Engl J Med, 2025 · PMID 40353578

  SURMOUNT-5, the head-to-head. Read it before assuming semaglutide is the strongest option.

• OZEMPIC (semaglutide) injection - US prescribing information, section 12.3 Novo Nordisk, DailyMed

  Source for every pharmacokinetic number above: 89% bioavailability, 12.5 L volume of distribution, 0.05 L/h clearance, greater than 99% albumin binding.

• RYBELSUS and OZEMPIC (oral semaglutide) tablets - US prescribing information Novo Nordisk, DailyMed

  Source for the 0.4-1% and 1-2% oral bioavailability figures and the SNAC absorption mechanism.