Understanding Tirzepatide Microdosing: How Much is a Micro Dose for You?

Last reviewed: June 16, 2026

Last updated: September 17, 2026

Written by: Jay Hastings, CEO of PlexusDx, and Jayden Lee, PharmD, EMBA, PlexusDx Medical Director

Jay Hastings is the CEO of PlexusDx, a precision health company focused on genetic testing, blood biomarker insights, and personalized wellness recommendations. He has more than 20 years of experience across healthcare innovation, genomics, laboratory operations, healthcare investing, and strategic finance.

Medically reviewed by: Jayden Lee, PharmD, EMBA

Jayden Lee, PharmD, EMBA, is the PlexusDx Medical Director, with a PharmD and MBA specializing in pharmacogenomics and clinical product development, with a proven ability to bridge the gap between genomic research and practical patient outcomes. Dr. Lee has more than 10 years of professional experience in clinical pharmacy, academia, and research.

This article is part of the PlexusDx Education Hub — your resource for evidence-based guidance on Peptides & GLP-1. Browse all Peptides & GLP-1 education

The most searched microdose question about tirzepatide is about one number: 1.25 mg. Is it a microdose? Does it work? This article gives the honest answer. Microdosing is not a medical term. In the PlexusDx study it meant a total weekly dose of 1 or 2 mg of injectable tirzepatide, below the usual 2.5 mg starting dose. The PlexusDx study did not test 1.25 mg as its own group, so we will tell you what it did test, and what it cannot say.

Why 1.25 mg comes up so often

The FDA-approved tirzepatide products, Zepbound® and Mounjaro®, start at 2.5 mg once a week per their labels. Half of 2.5 is 1.25. Many clinics that offer a “half dose” or a “microdose” simply cut the labeled starting dose in half. That is why 1.25 mg is the number people hear. It is not a labeled dose, and no trial has tested it on its own. Zepbound® and Mounjaro® are registered trademarks of Eli Lilly and Company. PlexusDx is not affiliated with or endorsed by Eli Lilly and Company.

What the PlexusDx study tested instead

PlexusDx looked back at records from its own care program. The medication was compounded injectable tirzepatide with vitamin B12 at a total weekly dose of 1 to 2 mg. Doses were grouped by the weekly total. Fifty-three of 60 patients started at 1 mg a week, and 7 of 60 started at 2 mg a week. There was no 1.25 mg group. So the study cannot say what 1.25 mg does. It can say what happened to people who started at 1 mg a week, which is a little less than 1.25 mg.

What happened to people who started at 1 mg a week

Among patients who started at 1 mg a week in total: 2.26% mean weight loss in the 14–35-day window (95% CI 1.63–2.90; n=51), 3.86% in the 36–59-day window (95% CI 2.83–4.90; n=18), and 6.10% in the 60–89-day window (95% CI 4.60–7.60; n=8). These groups are sorted by starting dose. Some patients later moved up to 2 mg a week, so this is not a “1 mg only” result.

The whole cohort of 60 looked similar: 2.18% mean loss in the 14–35-day window (n=57; median exposure 21 days), with 6 of 57 (10.5%) showing no loss or a gain. The full results, including the 36–59- and 60–89-day windows and the no-loss counts for each, are in microdose tirzepatide results at 3, 7 and 9 weeks.

How to read these numbers

Small groups. Short windows. No comparison group. Weights reported by patients, not measured in a clinic. Those are real limits, and the authors say so. The numbers describe a group. They do not predict what you would lose at 1 mg, 1.25 mg, or any dose. If you read a page that says a microdose “produces” a set number of pounds, ask for the study, the group size, and the time window. A number without those three things is a guess.

Who decides your dose

A licensed prescriber. In the PlexusDx program, an independent network of U.S.-licensed clinicians through a state-licensed telehealth platform reviews each intake and sets the dose, if any. You can ask about a low start. The clinician decides based on your health history, your BMI, your goals, and how you do on the medicine. Whether a dose moves up, stays, or stops is also the clinician’s call, made with you.

For what “microdose” means in general, see what is a microdose of tirzepatide. For schedule questions, see what happens if you take tirzepatide twice a week.

About the PlexusDx study

A retrospective, single-organization observational study of adults documented as new to GLP-1 medicines with BMI ≥27 kg/m²; no comparison group; self-reported weights; not a clinical trial; preprint not yet peer reviewed. The records came from the commercial care program that PlexusDx operates. Care was delivered by an independent network of U.S.-licensed clinicians through a state-licensed telehealth platform. The medication was compounded injectable tirzepatide with vitamin B12 at a total weekly dose of 1 to 2 mg, prepared by state-licensed compounding pharmacies operating in FDA-registered facilities. The study was written by Jay Hastings (PlexusDx CEO) and Jayden Lee, PharmD, EMBA (PlexusDx Medical Director). See the PlexusDx microdose tirzepatide study (60 patients, 2026).

The authors’ conclusion, in their words: “Weight loss was observed within the 14–35-, 36–59-, and 60–89-day observation windows among evaluable adults initiating compounded injectable tirzepatide at 1–2 mg/week. These hypothesis-generating observations support prospective comparative study, not conclusions about causality, equivalent dosing, or long-term safety.”

To our knowledge (as of September 2026), the first published patient cohort reporting outcomes for injectable tirzepatide started at 1 to 2 mg a week. The full preprint is on medRxiv: Weight Loss With Microdose Tirzepatide: Real-World Outcomes in Patients Initiating Treatment Below 2.5 mg Weekly (doi:10.64898/2026.09.15.26363172; posted September 17, 2026; CC BY 4.0). It has not yet been peer reviewed.

Competing interests, as stated in the preprint: “Jay Hastings is Chief Executive Officer of PlexusDx. Jayden Lee, PharmD, EMBA, is Medical Director of PlexusDx. PlexusDx operates the commercial care program from which the records analyzed in this study arose. The authors’ roles with PlexusDx constitute potential competing interests. The authors retained responsibility for the study design, analysis, interpretation of results, manuscript preparation, and decision to submit the work for publication. The authors and PlexusDx received no payments or services from any third party related to the submitted work.”

Where PlexusDx fits

PlexusDx offers compounded tirzepatide through its Weight Management Protocols, including the entry-tier Microdose GLP-1 Protocol. You fill out a short intake. A licensed clinician reviews it and decides what, if anything, fits you. The study described here looked back at records. It is not a promise of any result.

This article is educational. PlexusDx offers compounded tirzepatide through its Weight Management Protocols. The GLP-1 & Peptide Pathways Genetic Test analyzes how your genes influence peptide-related biological pathways. It does not recommend, prescribe, or determine which peptides you should use. Consult a qualified healthcare provider before beginning any peptide protocol. Compounded tirzepatide is not an FDA-approved drug product. It is prepared by state-licensed compounding pharmacies under federal compounding rules and is not the same as Zepbound® or Mounjaro®. Zepbound® and Mounjaro® are registered trademarks of Eli Lilly and Company. PlexusDx is not affiliated with or endorsed by Eli Lilly and Company.

Frequently Asked Questions

Is 1.25 mg tirzepatide effective?

No study has tested 1.25 mg as its own dose group, including the PlexusDx study. The closest data: patients who started at 1 mg a week in total lost a mean 2.26% in the 14–35-day window (95% CI 1.63–2.90; n=51). That describes a group, not what 1.25 mg will do for you.

Is 1.25 mg a microdose of tirzepatide?

By the common meaning, yes, because it is below the labeled 2.5 mg starting dose. Microdosing is not a medical term, though. In the PlexusDx study it meant a total weekly dose of 1 or 2 mg. Ask any clinic what number it means when it says microdose.

How much weight do people lose in the first weeks at 1 mg a week?

In the PlexusDx study, patients who started at 1 mg a week lost a mean 2.26% in the 14–35-day window (n=51). Across all 60 patients the mean was 2.18% (n=57; median exposure 21 days), or 4.4 lb, and 6 of 57 had no loss or gained weight.

Can I stay on a low dose of tirzepatide long term?

That is a prescriber’s decision. The PlexusDx study cannot answer it, because no patient had an eligible weight past 89 days, and the study did not look at long-term safety. Ask your clinician how they decide whether a dose stays the same, moves up, or stops.

Where does the 1 mg a week data come from?

From a retrospective, single-organization observational study of 60 adults documented as new to GLP-1 medicines, with BMI of 27 or higher, who started compounded injectable tirzepatide at 1 to 2 mg a week through the PlexusDx care program. It has no comparison group, uses self-reported weights, and is a preprint not yet peer reviewed.

This article is part of the PlexusDx Education Hub. Browse all Peptides & GLP-1 education

Medical and Editorial Standards

Medical review process: This article was reviewed for medical accuracy, scientific clarity, evidence alignment, and appropriate discussion of genetics, medications, supplements, biomarkers, and health-related claims.

Sources and evidence: PlexusDx educational content is developed using peer-reviewed research, clinical literature, reputable medical references, and, where applicable, public health or regulatory guidance.

Commercial transparency: PlexusDx offers genetic testing, blood biomarker testing, personalized supplement recommendations, and related precision wellness services. Product mentions are intended to help readers understand available options and should not be interpreted as medical advice.

Important disclaimer: PlexusDx educational content is for informational purposes only and should not be used as a substitute for professional medical advice, diagnosis, or treatment. Always consult a qualified healthcare provider before making decisions about medications, supplements, genetic testing, lab testing, or health-related care.