Tirzepatide Results Timeline: Week by Week Guide

Last updated: September 17, 2026

Written by: Jay Hastings, CEO of PlexusDx

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.

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

A week-by-week tirzepatide timeline sounds simple. It is not, because the evidence comes from very different places. This guide keeps two sources apart. First, what 60 patients on a low dose reported in the PlexusDx study, with group sizes and windows. Second, what full-dose clinical trials of the FDA-approved product reported, clearly labeled as separate. Do not read one as the continuation of the other. 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.

Weeks 1 to 2: nothing to report yet

The PlexusDx study did not count any weight taken before day 14. Early changes in appetite are commonly described, but this study has no data for the first two weeks and does not claim any.

Weeks 2 to 5 (days 14 to 35): what the PlexusDx study saw

Fifty-seven patients had a qualifying weight in this window; the median had been on treatment 21 days. Mean weight loss was 2.18% (95% CI 1.61–2.76; n=57; median exposure 21 days). Median loss was 1.96%. The study’s mean in pounds was 4.4 lb. Twelve of 57 (21.1%) had lost 3% or more, and 5 of 57 (8.8%) had lost 5% or more. Six of 57 (10.5%) had no loss or gained weight: 1 at exactly 0% and 5 who gained.

An older version of this guide said weeks 1 to 3 usually bring “1 to 3 pounds.” That figure had no source. It has been replaced with the study result above.

Weeks 5 to 8 (days 36 to 59): a smaller group

Nineteen patients had a qualifying weight here; the median exposure was 48 days. Mean loss was 3.58% (95% CI 2.43–4.72; n=19); median 3.59%; the study’s mean in pounds was 6.9 lb. Eleven of 19 (57.9%) had lost 3% or more and 5 of 19 (26.3%) had lost 5% or more. Two of 19 (10.5%) had no loss or gained: 1 at 0% and 1 who gained.

Weeks 9 to 13 (days 60 to 89): eight patients

Only 8 patients had a qualifying weight in this window; the median exposure was 65.5 days. Mean loss was 6.10% (95% CI 4.60–7.60; n=8); median 5.88%; the study’s mean in pounds was 12.2 lb. All 8 (100.0%) had lost 3% or more, and 6 of 8 (75.0%) had lost 5% or more. None had no loss or a gain. Eight people is a small group, and the interval is wide.

Read the three windows carefully

These are not one group followed over time. The same person can appear in more than one window, and many people appear in only the first. Sixteen patients were in both of the first two windows; their mean loss moved from 2.20% to 4.10%, a paired difference of 1.91 percentage points (95% CI 1.17–2.64; nominal P<0.001). Seven of them reached all three windows, at 2.36%, 4.72% and 6.42%. A model using all 93 eligible weights estimated 2.16 percentage points more loss per 30 days on treatment (95% CI 1.69–2.63; nominal P<0.001). That is an association over the observed follow-up, not a causal effect. Full details: microdose tirzepatide results at 3, 7 and 9 weeks.

After week 13: no PlexusDx data

No eligible observation in the study reached 90 days. Anything about months 4 and beyond has to come from other sources, and it cannot be joined to the numbers above.

Separate evidence: full-dose clinical trials

The FDA approval of Zepbound® rested on the SURMOUNT trials of tirzepatide at 5, 10 and 15 mg a week. In SURMOUNT-1, as published in the New England Journal of Medicine in 2022, adults with obesity or overweight who did not have diabetes had mean weight changes at 72 weeks of about 15.0% at 5 mg, 19.5% at 10 mg and 20.9% at 15 mg, versus about 3.1% with placebo, alongside diet and exercise. Those were measured weights, in a randomized trial with a placebo group, at doses several times the PlexusDx study’s, over about a year and a half.

That is a different world from a 60-patient look-back with self-reported weights and no comparison group. The trial numbers do not tell you what a 1 to 2 mg dose does at week 72, and the PlexusDx numbers do not tell you what a labeled dose does at week 3. Keep them apart. Zepbound® and Mounjaro® are registered trademarks of Eli Lilly and Company. PlexusDx is not affiliated with or endorsed by Eli Lilly and Company.

Side effects along the way

At the first eligible check-in in the PlexusDx study, 11 of 58 patients (19.0%) reported any side effect: nausea 7 of 58, constipation 6 of 58, diarrhea 2 of 58, vomiting 0 of 58. Two of 60 had no matched check-in and are counted as unknown. These are routine check-in answers, not systematic surveillance, and they do not describe a peak week. Per the FDA label, stomach side effects are most common when starting and when the dose rises. More in side effects people reported at 1 to 2 mg.

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

When do you see results on tirzepatide?

It depends on the dose and the person. In the PlexusDx study of 1 to 2 mg a week, the mean loss in the 14–35-day window was 2.18% (n=57; median exposure 21 days), or 4.4 lb, and 6 of 57 had no loss or gained. Before day 14, the study has no data.

How much weight do people lose on tirzepatide in 3 months?

The PlexusDx study’s last window, 60–89 days, had 8 patients with a mean loss of 6.10% (95% CI 4.60–7.60; median exposure 65.5 days), or 12.2 lb. That is a small group at a low dose. Full-dose trial results at 72 weeks are a separate, non-comparable source.

Can I combine the PlexusDx numbers with SURMOUNT trial numbers to build a timeline?

No. The trials used measured weights, placebo groups, doses of 5 to 15 mg, and 72 weeks of follow-up. The PlexusDx study used self-reported weights, no comparison group, 1 to 2 mg a week, and windows under 90 days. Joining them would create a timeline no study supports.

Did everyone in the PlexusDx study lose weight over time?

No. Six of 57 in the 14–35-day window and 2 of 19 in the 36–59-day window had no loss or gained weight. None of the 8 in the 60–89-day window did. Fewer patients reached the later windows, so those results carry more uncertainty than the first.

What happens after week 13 on a low dose?

The PlexusDx study cannot say; no eligible observation reached 90 days. Whether a dose stays, rises or stops after that is a prescriber’s decision. Any long-term numbers you read come from other sources and cannot be joined to this study’s early windows.

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

Medical and Editorial Standards

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.