Guides
These guides cover what GLP-1 medications are, how semaglutide and tirzepatide each work, and the specific numbers behind retatrutide’s dosage and side effects. Start with the mechanism guides if you are new to the class, jump straight to the retatrutide guides if you already know the basics and want the trial data, or use the reconstitution calculator if you just need the arithmetic. Every guide below cites the trial it draws from by name, with a resolvable DOI link, rather than a percentage with no source behind it, and every one states its trial’s limits, open-label design, industry funding, placebo comparison rather than a head-to-head, next to the number rather than leaving them out.
Once you know how the drugs work, the next decision is which one to ask a prescriber about and where to get it: the two links at the bottom of this page cover exactly that.
What are GLP-1 medications?
The overview guide to start with: what activating the GLP-1 receptor actually does in the body, and why semaglutide, tirzepatide and retatrutide are discussed together even though only two of the three can legally be prescribed. It also lays out the class in tiers, one receptor, two receptors, three receptors, and shows how that structure predicts the weight-loss numbers that follow. Read what are GLP-1 medications.
How semaglutide works
Semaglutide activates a single hormone receptor, GLP-1, and this guide states its 72-week trial result plainly rather than softening it: 13.7% mean weight loss, the lower of the two figures in the only head-to-head trial that exists. It also covers the real reason semaglutide still has a genuine case behind it, a longer approval and prescribing track record than tirzepatide. Read how semaglutide works.
How tirzepatide works
The dual-receptor mechanism, and why it beat semaglutide by 6.5 percentage points in the only head-to-head trial that has ever compared them, 20.2% versus 13.7% at 72 weeks. The guide also states the trial’s two disclosed limits, open-label and Eli Lilly-funded, next to that number rather than leaving them out. Read how tirzepatide works.
Retatrutide dosage
The exact titration schedule from retatrutide’s own phase 2 trial: six dose arms, starting as low as 1 mg and stepping up every 4 weeks toward a 12 mg target that produced 24.2% mean weight loss at 48 weeks. This is trial-protocol data, not a prescribing guideline, since retatrutide remains investigational. Read retatrutide dosage.
Retatrutide side effects
What the phase 2 trial actually reported: gastrointestinal side effects that were dose-related and partially eased by a lower 2 mg starting dose, plus a heart-rate finding, a rise that peaked at 24 weeks and then declined, that most competing pages only report half of. The guide also states plainly that no trial has compared retatrutide’s side-effect profile against semaglutide’s or tirzepatide’s directly, so any ranking of the three by safety is not something the evidence currently supports. Read retatrutide side effects.
Reconstitution calculator
The arithmetic behind “how much bacteriostatic water” searches, worked out for any vial strength and dose: a 10 mg vial with 1 mL of water yields 10 mg/mL, so a 2 mg dose measures 0.2 mL, or 20 units on a standard U-100 syringe. Educational reference only, not a dosing recommendation, since retatrutide cannot legally be prescribed. Use the reconstitution calculator.
Start here if you are choosing a treatment
Once the mechanism is clear, the decision that is actually left is which FDA-approved drug to ask about and which provider to get it from. Our semaglutide vs tirzepatide comparison lays out the trial numbers side by side, with the open-label and funding caveats stated plainly. Our provider reviews score the five providers this site covers against one published rubric, so the choice is not a guess.
What you can be prescribed today
Semaglutide and tirzepatide are both FDA-approved and available today from a licensed prescriber after a medical evaluation; retatrutide is not an option outside a clinical trial. The providers below evaluate eligibility and prescribe compounded semaglutide or compounded tirzepatide.
These providers prescribe tirzepatide and semaglutide, which are FDA-approved. We may earn a commission, and it never changes your price.
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#1
TrimRxPersonalized programs, US pharmacies
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#2
Joi & BlokesHis & hers compounded GLP-1s
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#3
ReadyRxFast approvals on weight-loss meds
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