GLP-1s:
What Actually Works, What Goes Wrong, and How to Stay on Past Year One

GLP-1 (glucagon-like peptide-1) is an incretin hormone secreted by intestinal L-cells in response to food. It triggers four physiologic effects that, taken together, make these drugs work:

1. Slows gastric emptying. Food sits in the stomach longer; satiety signals last longer.
2. Suppresses postprandial glucagon. Glucose excursions after meals flatten.
3. Stimulates insulin secretion in a glucose-dependent way. Lower hypoglycemia risk than older diabetes drugs.
4. Acts on hypothalamic appetite centers. Reduces hunger signaling and the constant background-process people call food noise, the intrusive thoughts about food that dominate decision-making at higher BMI states. The disappearance of food noise is what most patients describe as the drugs' single most important effect.

The pharmacological design lineage runs in three generations:

• Single agonist (GLP-1 only), semaglutide. Native GLP-1 receptor signaling.
• Dual agonist (GLP-1 + GIP), tirzepatide. GIP (glucose-dependent insulinotropic polypeptide) layered on adds metabolic effects on insulin sensitivity and lipid handling, and the dual receptor binding gives a higher efficacy ceiling.
• Triple agonist (GLP-1 + GIP + glucagon), retatrutide. Glucagon receptor activation drives energy expenditure (lipolysis, mild thermogenesis) on top of the appetite suppression. Not yet FDA-approved as of 2026; in late phase 3.

Adding receptors raises efficacy but also broadens the side-effect surface. Glucagon agonism in retatrutide drives stronger fat-loss effects but also produces a different signature on resting heart rate and a unique nausea profile at higher doses than tirzepatide.

Semaglutide

• Brand names: Ozempic (T2D, US 2017), Wegovy (obesity, US 2021), Rybelsus (oral T2D).
• Receptor: GLP-1 only.
• Half-life: ~7 days. Once weekly.
• Pivotal weight-loss trial: STEP-1, 14.9% weight loss at 68 weeks at 2.4 mg vs 2.4% placebo.
• Cardiovascular outcomes trial: SELECT (2023), semaglutide 2.4 mg in 17,604 patients with obesity and prior CVD without diabetes. 20% reduction in the composite primary endpoint (CV death, non-fatal MI, non-fatal stroke), HR 0.80, with 9.4% mean weight reduction at 39.8 months ^[1]. The first GLP-1 to show MACE reduction in non-diabetic obesity.

The longest real-world track record. The default starting compound for most people unless cost, response, or specific side-effect history pushes elsewhere.

Tirzepatide

• Brand names: Mounjaro (T2D, US 2022), Zepbound (obesity, US 2023).
• Receptor: GLP-1 + GIP dual agonist.
• Half-life: ~5 days. Once weekly.
• Pivotal weight-loss trial: SURMOUNT-1, 72-week weight loss of 16.0%, 21.4%, and 22.5% at 5/10/15 mg vs 2.4% placebo. 89.4–96.3% achieved ≥5% loss ^[2].
• Body composition data (SURMOUNT-1): higher fat-mass-to-lean-mass loss ratio than semaglutide-class trials.

Higher efficacy ceiling than semaglutide and (in head-to-head SURMOUNT-5) superior weight loss vs semaglutide 2.4 mg. Often the second compound people land on after a semaglutide response that plateaus.

Retatrutide

• Brand name: none yet, investigational, late phase 3 as of 2026.
• Receptor: GLP-1 + GIP + glucagon triple agonist.
• Half-life: ~6 days. Once weekly.
• Pivotal weight-loss trial (TRIUMPH-4): ~28.7% weight loss at 12 mg over 48 weeks vs 22.5% on tirzepatide. Body composition data favorable on fat-vs-lean ratio because the glucagon arm raises energy expenditure.

Not yet FDA-approved. Available primarily through compounded supply, which is now in narrower regulatory standing than it was in 2024 (covered below). For users currently running it, run as if FDA approval is the eventual outcome, but track expecting that supply chain access may shift.

Orforglipron

• Brand name: none yet, Lilly investigational, FDA submission in progress as of late 2025/early 2026.
• Receptor: GLP-1 only (oral small molecule, not a peptide).
• Dosing: once daily, oral. Not subject to the food-fasting constraints of oral semaglutide (Rybelsus).
• Pivotal weight-loss trial (ATTAIN-1): 12.4% (~27.3 lbs) weight loss at 72 weeks at the highest dose. 59.6% achieved ≥10% loss; 39.6% achieved ≥15% ^[3]. ATTAIN-2 in T2D showed 10.5% weight loss with 1.8% HbA1c reduction.

The structural innovation here is oral dosing without the peptide-degradation problem. As a small molecule it doesn't need an injection or a complex absorption-enhancer formulation. Lower efficacy ceiling than tirzepatide, similar safety profile. Likely role: lower-friction starting compound for patients who refuse injections or have lower weight-loss targets.

Quick comparison

The default decision tree:

• Start at semaglutide if cost, insurance coverage, or familiarity dominate. Decade of real-world data, established CV outcomes signal, broadest provider comfort.
• Start at tirzepatide if your weight-loss target requires the higher efficacy ceiling, you have insurance or cash flow that supports it, or you have a documented poor response to semaglutide.
• Start at retatrutide if you understand and accept its investigational status, the supply-chain volatility, and the slightly different side-effect profile (more glucagon-driven RHR elevation, more pronounced nausea at peak titration). Not a default.
• Start at orforglipron when it lands FDA approval if injections are the barrier and your target is in the 10–15% loss range.

Standard titration

The lesson the field learned across SURMOUNT, STEP, and the early compounded era: faster titration drives higher dropout via GI side effects, not faster weight loss. The published titration schedules exist for a reason.

Microdosing and split-dosing

A growing subset of users run smaller doses more frequently, typically 2× weekly at half the standard dose, or daily microdoses of compounded compounds. The pharmacokinetic argument is real: weekly dosing produces a meaningful peak-to-trough swing, and many people experience a Friday/Saturday hunger return that is often misread as the drug failing. More frequent, smaller doses flatten the curve.

The trade is operational complexity (more injections to track, more sites to rotate) and, for compounded versions, the math required to split a vial accurately. The OptiPin peptide calculator handles compounded GLP-1 reconstitution and dose-splitting math with one-tap presets for common protocols.

The microdosing-as-titration approach also softens GI side effects in users who could not tolerate the standard escalation schedule.

GI: nausea, sulfur burps, constipation, diarrhea, gastroparesis

The headline side effect category and the single most common reason for discontinuation. The mechanism is the same as the therapeutic mechanism: delayed gastric emptying.

• Nausea peaks during titration steps and typically subsides 1–2 weeks after each dose increase. Eating smaller meals, eating slowly, and avoiding high-fat meals during peak windows are the practical levers.
• Sulfur burps, egg-smelling eructation, are a specific signature of delayed gastric emptying allowing protein-fermentation byproducts to accumulate. Triggered by high-protein, high-fat, or high-sulfur foods (eggs, broccoli, garlic, dairy). Mitigations: smaller portion size, ginger, food simplification, splitting weekly dose. The fastest way to identify your specific triggers is daily side-effect logging tied to meal notes, OptiPin's daily check-in captures GI symptoms with severity and free-text notes so you can see, after 2–3 weeks, which foods cluster with sulfur-burp days vs. clean days.
• Constipation is the slow-burn complaint. Magnesium, fiber, hydration, and walking address most of it; bisacodyl/Miralax for the resistant cases.
• Diarrhea is less common than constipation but occasionally appears, often during early titration.
• Severe and persistent vomiting or new-onset epigastric pain warrants discontinuation and workup, this is the gastroparesis/pancreatitis red-flag zone.

Hair loss (telogen effluvium)

The mechanism is rapid weight loss, not the drug per se. Caloric deficit and the metabolic stress of fast loss push hair follicles into the resting (telogen) phase; shedding shows up 2–4 months later. Recovery follows the same timeline reversed once weight stabilizes. Adequate protein, biotin, iron, and avoiding aggressive caloric deficits at peak titration reduce the severity. This is identical in mechanism to post-pregnancy and post-bariatric-surgery shedding. The shedding window is also the place where progress photos earn their keep, OptiPin's progress photo capture (with cloud storage and side-by-side before/after) gives you a 1080×1080 visual of hair density and overall body composition that matters when month 4 is the worst-feeling month and the bathroom mirror is lying to you.

Muscle / lean mass loss

The single most actionable problem on this list. Without intervention, lean tissue accounts for roughly 26–40% of total weight loss in the major trials ^[4]. Mitigation is the same protocol regardless of which compound:

• Resistance training 3–5×/week. Compound movements, progressive overload, no exceptions.
• Protein 1.6 g/kg of body weight (or higher). Per fat-free mass scaled, that's 1.6–2.3 g/kg of lean tissue. Spread across 4–5 meals.
• Slower titration when possible. Faster weight loss → higher lean-to-fat-loss ratio.
• TRT-adjacent protocols in men with low-T patterns can attenuate the lean-mass loss further (covered in the TRT pillar and the cross-cut "GLP-1 + TRT" framing).

The patient who maintains lean mass on these drugs is not the patient who eats nothing because they aren't hungry. They're the patient who lifts and meets a protein floor regardless of appetite. OptiPin pulls weight, body fat percentage, and resting heart rate directly from Apple Health (or Google Health Connect) and overlays compound dose changes on the trend line, so the question "did the lean-mass loss accelerate when I jumped to 10 mg" becomes a visible chart instead of a worry.

Resting heart rate elevation

Modest RHR increase (typically 2–5 bpm) is a class effect, more pronounced on tirzepatide and retatrutide than semaglutide. Trace it via wearables; if the magnitude exceeds 10 bpm or symptoms (palpitations, lightheadedness) appear, raise it with your prescriber. Not a discontinuation trigger in most cases, but worth tracking.

Plateau dynamics

Plateaus are physiologic adaptation, not the drug "stopping working." The body downregulates basal metabolic rate proportional to weight loss and increases efficiency. Managing through a plateau:

• Confirm it's a plateau (3–4 weeks of stable weight at consistent intake), not a noise window.
• Audit calories, appetite suppression makes most people think they're still eating less than they are. The bathroom scale is more honest than the food memory.
• Increase activity before increasing dose. NEAT (non-exercise activity thermogenesis) is the largest underexploited lever.
• If genuinely stuck for 6+ weeks at a sub-target weight, dose increase is the legitimate next move.

The "is this actually a plateau" question is where the AI summary in OptiPin earns its weight. It reads the weight trend, the dose log, the daily symptom and hunger check-ins, and the Apple Health activity data together, then tells you whether you're looking at a 3-week stall (noise), a 6-week genuine plateau (intervention warranted), or appetite-suppression decay that's about to resolve at the next titration. The month-in-review summary surfaces the same picture as a narrative once a month so the trajectory is visible without you having to interpret three charts at once.

Trough-week hunger return

Common pattern: smooth Monday-Wednesday after the weekly shot, hunger and food-noise return Friday-Saturday. This is dose-curve, not failure. Mitigations: split the weekly dose into 2× per week, or move to daily microdosing. The trough hunger is the single most actionable case for moving off a once-weekly schedule. OptiPin's estimated-levels visualization models the GLP-1 concentration curve between doses based on the compound's half-life and your actual injection log, so the trough window, and exactly how deep it gets before the next shot, is visible as a chart. Users who switch to twice-weekly typically do so after seeing the Friday-night drop in their own data, not after reading about it.

Other monitorable items

• Gallbladder events, rapid weight loss elevates gallstone risk independent of the drug.
• Pancreatitis, rare but real. New severe upper abdominal pain warrants immediate workup.
• Diabetic retinopathy progression, documented in T2D populations rapidly improving glycemic control; not relevant for non-diabetic obesity use.

Semaglutide ↔ tirzepatide

The most common switch. Approximate dose equivalency (community-derived; not regulator-published):

Practically: switch on the standard dosing day, no washout required. Take the equivalent or one-step-lower tirzepatide dose for the first 2–4 weeks and assess. Most users report less GI on the switch than they expected, because they're already adapted to the class.

Tirzepatide → retatrutide

The retatrutide community standard is a 1–2 week washout from tirzepatide before starting at 2 mg retatrutide, then standard titration. Going faster increases the likelihood of nausea and RHR signal.

Switching back

Cleanly possible in either direction. The semaglutide-to-tirzepatide-and-back cycle is well-documented in real-world use; retatrutide-back-to-tirzepatide is similar. Plan as if you're starting at a one-step-lower dose of the new compound for the first 2 weeks, then re-titrate.

What the trial data shows

The hardest-earned lesson of the GLP-1 era: weight regain when you stop is fast and substantial.

• STEP-1 extension data: stopping semaglutide led to roughly two-thirds of lost weight regained over the year following discontinuation.
• SURMOUNT-4 (tirzepatide maintenance): patients who continued tirzepatide maintained their weight loss; those switched to placebo regained meaningfully over the trial period.
• ATTAIN-MAINTAIN (orforglipron, Dec 2025 topline): orforglipron successfully maintained weight loss in patients who had achieved their loss on injectable GLP-1s, the first dedicated GLP-1 maintenance trial with a positive readout.

The honest framing: GLP-1s are increasingly understood as chronic medications for a chronic condition (obesity), not weight-loss courses with a finish line. The mental model that worked for behavioral diet attempts ("hit the goal, then move on") doesn't transfer.

Maintenance strategies that work in practice

• Maintenance dose reduction. Most users land at 50–75% of their loss-phase dose for maintenance. Drop in 0.5-step decrements over 8–12 weeks.
• Dose spacing. Q10D or Q14D dosing (instead of Q7D) keeps appetite suppression with less drug exposure for users who tolerate longer windows.
• Behavioral consolidation. The maintenance window is where the protein and resistance-training disciplines transition from "supports the drug" to "is the protocol." Lifestyle changes that hold without the drug are the goal.
• Tracking matters more on maintenance, not less. The slow regain pattern is the most insidious, half a pound a week feels like nothing until it's 25 pounds in 12 months. The OptiPin month-in-review surfaces this directly, a single monthly summary covering weight trajectory, dose adherence, and protocol changes, with an explicit flag when the trend deviates from your maintenance baseline. The slow regain is the failure mode this is built for.

The compounding landscape changed substantially between 2023 and 2026 and is the question that dominates real-world access decisions.

What changed

• 2022–2023: Semaglutide and tirzepatide were placed on FDA's drug shortage list. Section 503A and 503B compounding pharmacies could legally produce non-branded versions during the shortage.
• 2024: FDA declared the tirzepatide shortage resolved. Compounded tirzepatide lost its shortage-pathway status, with enforcement discretion phased out over months.
• Late 2024–early 2025: Same trajectory for semaglutide.
• 2025–2026: The licensed compounding channel for branded-equivalent GLP-1s closed in most cases. The market response was migration to gray-market "research peptide" sourcing, the same QC concerns covered in the peptides pillar under sourcing risk.

The retatrutide situation is structurally different: it's still investigational, never had a "shortage" because it was never approved, and has always been in the gray-market lane for non-trial users.

Access by route

• Insurance-covered branded, Wegovy, Zepbound, Ozempic, Mounjaro through pharmacy benefit. Often the cheapest path if you have coverage; often impossible if you don't (cash prices around $1,000–$1,300/month US).
• Telehealth direct-to-consumer, many platforms shifted from compounded supply to FDA-approved supply during 2024–2025, with adjusted pricing.
• Licensed compounding pharmacies, narrowed dramatically post-shortage resolution. Some jurisdictional and clinical-need exceptions remain.
• Gray-market / research peptide, same QC and legal questions as for any unregulated peptide source. See the country-specific GLP-1 access guide for jurisdiction-specific frameworks.

Reconstitution math

Compounded GLP-1s ship as lyophilized powder requiring bacteriostatic water reconstitution. The math is identical to peptide reconstitution and is fully covered by the OptiPin peptide calculator, which has dedicated presets for semaglutide, tirzepatide, and retatrutide vials at common concentrations. For technique, see the peptide guide.