Microdose Tirzepatide Results at 3, 7 and 9 Weeks: What Our Study Saw

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

This article reports what the PlexusDx microdose tirzepatide study saw in three time windows. The windows had median exposures of 21, 48 and 65.5 days. That is roughly 3, 7 and 9 weeks, which is why the title says so. Every number below carries its group size and its window. 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.

One rule first. This was not a clinical trial. There was no comparison group. Weights were self-reported. The same person can appear in more than one window. Please read the numbers with those limits in mind, or start with what “hypothesis-generating” means.

Who was in the study

Sixty adults who were new to GLP-1 medicines and had a BMI of 27 or higher. Their mean age was 47.3 years (SD 11.0). Forty-nine of 60 (81.7%) were women. Mean starting BMI was 33.3 kg/m² (SD 6.1); the median was 31.4 (IQR 28.7–36.1). Mean starting weight was 205.7 lb (SD 47.6). All 60 started on compounded injectable tirzepatide with vitamin B12 at a total weekly dose of 1 to 2 mg. Fifty-three of 60 (88.3%) started at 1 mg a week in total, and 7 of 60 (11.7%) started at 2 mg a week in total.

The three windows

The study grouped each patient’s latest eligible weight into windows by days since the first dose: 14 to 35 days, 36 to 59 days, and 60 to 89 days. No eligible weight reached 90 days, so there is nothing to report past that point.

Window	Patients (n)	Median days on treatment	Mean weight loss (95% CI)	Median loss	Mean pounds lost	Lost 3% or more	Lost 5% or more
14–35 days (about 3 weeks)	57	21	2.18% (1.61–2.76)	1.96%	4.4 lb	12/57 (21.1%)	5/57 (8.8%)
36–59 days (about 7 weeks)	19	48	3.58% (2.43–4.72)	3.59%	6.9 lb	11/19 (57.9%)	5/19 (26.3%)
60–89 days (about 9 weeks)	8	65.5	6.10% (4.60–7.60)	5.88%	12.2 lb	8/8 (100.0%)	6/8 (75.0%)

In words: 2.18% mean weight loss in the 14–35-day window (n=57; median exposure 21 days). 3.58% mean weight loss in the 36–59-day window (n=19; median exposure 48 days). 6.10% mean weight loss in the 60–89-day window (n=8; median exposure 65.5 days). The pound figures are the study’s own means, not recomputed from the percentages.

Not everyone lost weight

Averages hide people. In the 14–35-day window, 6 of 57 patients (10.5%) had no loss or gained weight: 1 stayed at exactly 0% and 5 gained. In the 36–59-day window, 2 of 19 (10.5%) had no loss or gained: 1 at 0% and 1 gained. In the 60–89-day window, 0 of 8 had no loss or gain. Fewer people reached the later windows, so those groups are small and the numbers are less certain.

Why the later windows are not “better results”

It is tempting to read the table as one group getting better over time. It is not one group. Fifty-seven people had a weight in the first window, 19 in the second, and only 8 in the third. Some of the same people appear in two or three windows. Others stopped, moved above 2 mg a week, or had no qualifying weight yet. The study did not fill in any missing numbers.

The study did look at people who appeared in more than one window. Sixteen patients had a selected weight in both the 14–35- and 36–59-day windows. Their mean loss went from 2.20% to 4.10%, a mean paired difference of 1.91 percentage points (95% CI 1.17–2.64; nominal P<0.001). Seven of those 16 were in all three windows, with mean losses of 2.36%, 4.72% and 6.42%. A model using all 93 eligible weights estimated 2.16 percentage points more weight loss per 30 days on treatment (95% CI 1.69–2.63; nominal P<0.001). That is an association over the time people were watched. It is not proof the drug caused it.

What about the 1 mg per week group?

Most patients started at 1 mg a week. Among those who started at 1 mg a week in total, mean loss was 2.26% at 14–35 days (95% CI 1.63–2.90; n=51), 3.86% at 36–59 days (95% CI 2.83–4.90; n=18), and 6.10% at 60–89 days (95% CI 4.60–7.60; n=8). These are grouped by starting dose. Some of these patients later moved up to 2 mg a week.

What the study cannot tell you

It cannot tell you what you will lose. It cannot say a 1 to 2 mg dose works as well as a higher dose, because no higher-dose group was studied. It cannot be set next to a clinical trial of the FDA-approved product, because trials use different patients, measured weights, a placebo group, and much longer follow-up. It cannot speak to safety past 89 days. What it can do is describe, honestly, what 60 real patients reported over their first weeks, and make the case for a proper prospective study. Details of how the records were checked are in how we checked the data. The first window on its own is covered in first month on microdose tirzepatide.

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

How much weight did people lose on microdose tirzepatide in the PlexusDx study?

Mean loss was 2.18% in the 14–35-day window (n=57; median exposure 21 days), 3.58% in the 36–59-day window (n=19; 48 days) and 6.10% in the 60–89-day window (n=8; 65.5 days). In pounds, the study’s own means were 4.4, 6.9 and 12.2 lb.

Did everyone in the study lose weight?

No. In the 14–35-day window, 6 of 57 patients (10.5%) had no loss or gained weight. In the 36–59-day window, 2 of 19 (10.5%) did. In the 60–89-day window, 0 of 8 did. Averages describe a group. They do not describe what will happen to one person.

Is this study as strong as a clinical trial?

No. It is a retrospective, single-organization observational study with no comparison group and self-reported weights. It is a preprint not yet peer reviewed. The authors call the findings hypothesis-generating: they support running a prospective comparative study, not drawing conclusions about cause, equivalent dosing or long-term safety.

How many people were on 1 mg versus 2 mg a week?

Fifty-three of 60 (88.3%) started at 1 mg a week in total, all as 1 mg once weekly. Seven of 60 (11.7%) started at 2 mg a week in total: four took 1 mg twice weekly and three took 2 mg once weekly. Dose was classified by the weekly total, not per injection.

Where can I read the full study?

The study hub page on plexusdx.com summarizes the cohort, methods and results and is updated about every six weeks. The full manuscript has been submitted to medRxiv, a preprint server. Once the public preprint is live, this page will link to its DOI so every number can be checked at the source.

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.