Research Guide
A clear GLP-1 dosing guide covering semaglutide, tirzepatide and retatrutide titration, microdosing questions, syringe math and side effects.
If you are researching GLP-1 dosing, this class is different from most peptides discussed online: large randomised human trials mean the numbers people quote can be traced to a protocol. It also means these are approved or investigational prescription medicines, not research curiosities.
Educational and research information only. Nothing here is medical advice, prescribing guidance or a recommendation to use any compound. Consult a licensed healthcare professional before any health decision.
The defining feature of this class is the escalation schedule. Trials moved in steps of roughly four weeks, holding a dose only as long as tolerability allowed:
Holding at a lower step is a normal trial behaviour, not a failure. The maximum studied dose is a ceiling, not a goal.
Microdosing is an informal term people use for doses below the published starting amount or for slower-than-trial escalation. It is not a standardized clinical protocol, and controlled trial evidence supports scheduled titration rather than informal microdosing. For that reason, this guide treats microdosing as a terminology question, not as a validated dosing method.
Because doses here are small in volume, concentration choice matters more than with repair peptides:
Pick a concentration that puts the target dose on a clearly readable unit mark. Add the water slowly down the vial wall, swirl rather than shake, and refrigerate after mixing.
Nausea, vomiting, diarrhoea, constipation and reflux are the dominant reported effects and are dose- and escalation-dependent. Trials responded by slowing escalation rather than adding medication. Pancreatitis and gallbladder disease appear in the safety literature, and significant lean-mass loss alongside fat loss is a recurring finding, which is why protein intake and resistance training are discussed constantly around this class.
Rodent thyroid C-cell tumour findings underpin a contraindication for anyone with a personal or family history of medullary thyroid carcinoma or MEN2.
Published research reference
Half-life: That binding slows clearance and stretches the half-life to about 7 days, which is why one weekly injection is enough.
Trial / research dose bands
Cited studies
Educational research reference only — not medical advice.
Published research reference
Half-life: Tirzepatide has a 5-day half-life.
Trial / research dose bands
Reported side effects
Cited studies
Educational research reference only — not medical advice.
Published research reference
Half-life: The longer circulation time is the technical reason for the ~6-day half-life and once-weekly dosing.
Trial / research dose bands
Reported side effects
Cited studies
Educational research reference only — not medical advice.
Published research reference
Trial / research dose bands
Reported side effects
Cited studies
Educational research reference only — not medical advice.
What is GLP-1?
GLP-1 is an incretin hormone released after eating. Its receptor agonists slow gastric emptying, increase glucose-dependent insulin release and act on appetite signalling in the brain, which is why reduced food intake is the dominant effect people notice.
What is microdosing GLP-1?
Microdosing is an informal term for using amounts below published starting doses or increasing more slowly. It has no standardized clinical definition, and the controlled evidence base describes scheduled titration rather than informal microdosing.
How do semaglutide, tirzepatide and retatrutide differ?
Semaglutide is a single-receptor GLP-1 agonist. Tirzepatide is a dual GIP/GLP-1 agonist. Retatrutide is a triple GLP-1/GIP/glucagon agonist still in clinical development. Broadly, adding receptors has produced larger trial weight-loss figures and, in most reports, more dose-dependent gastrointestinal effects.
Where do cagrilintide and survodutide fit?
Cagrilintide is a long-acting amylin analogue, not a GLP-1 agonist; it is studied on its own and paired with semaglutide as CagriSema. Survodutide is a dual glucagon/GLP-1 agonist in trials. Both are investigational.
Why does titration matter so much?
Trial protocols step doses up over weeks rather than starting at target because gastrointestinal tolerability, not efficacy, is the limiting factor. Escalating too quickly is the single most common cause of nausea, vomiting and abandoned protocols.
What do published titration schedules look like?
Semaglutide trials began at 0.25 mg weekly, stepping roughly every four weeks through 0.5, 1.0, 1.7 and up to 2.4 mg weekly. Tirzepatide began at 2.5 mg weekly, stepping every four weeks through 5, 7.5, 10, 12.5 and up to 15 mg weekly. Retatrutide trial arms escalated monthly toward targets of 4, 8 and 12 mg weekly. These are trial designs, not prescribing instructions.
How is a GLP-1 vial reconstituted?
Divide vial strength by the water volume added. A 5 mg semaglutide vial with 2 mL of bacteriostatic water gives 2.5 mg/mL, so 0.25 mg is 0.1 mL — 10 units on a U-100 syringe. Small doses at high concentration are easy to mis-draw, so the concentration should be chosen so the target dose lands on a readable unit mark.
What are the main safety concerns?
Nausea, vomiting, constipation and reflux are the common effects. Pancreatitis, gallbladder disease and significant lean-mass loss appear in the safety literature, and rodent thyroid C-cell tumour findings drive a contraindication for personal or family history of medullary thyroid carcinoma or MEN2. These are prescription medicines; this class in particular belongs under clinical supervision.
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