Side Effects People Reported at 1 to 2 mg: What 58 Check-Ins Said

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

Tirzepatide side effects are one of the most searched topics about the drug. This article does two things. It lists what the FDA label warns about, for any dose. Then it reports what 58 patients on a much lower dose said at their first check-in in the PlexusDx study. 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.

What the FDA label lists

Per the labels for Zepbound® and Mounjaro®, the most common side effects are nausea, diarrhea, vomiting, constipation, stomach pain, indigestion, injection-site reactions, tiredness, allergic reactions, burping, hair loss, and heartburn. The label also carries a boxed warning about thyroid C-cell tumors seen in rodent studies, and warnings about pancreatitis, gallbladder problems, low blood sugar when used with insulin or sulfonylureas, kidney injury from dehydration, severe stomach problems, and others. Read the label or the medication guide, and talk to your prescriber. Zepbound® and Mounjaro® are registered trademarks of Eli Lilly and Company. PlexusDx is not affiliated with or endorsed by Eli Lilly and Company.

Compounded tirzepatide is the same molecule, so the label’s warnings are the right starting point at any dose. A lower dose does not remove them.

What 58 patients reported at their first check-in

The PlexusDx study matched each patient’s first eligible check-in to their record. Matched answers existed for 58 of 60 patients. Two of 60 were missing or could not be matched. Those two are not counted as symptom-free; they are counted as unknown.

• Any reported side effect: 11 of 58 (19.0%)
• Nausea: 7 of 58 (12.1%)
• Constipation: 6 of 58 (10.3%)
• Diarrhea: 2 of 58 (3.4%)
• Vomiting: 0 of 58 (0.0%)
• Said they felt good or excellent overall: 57 of 58 (98.3%)

Symptoms are not mutually exclusive. One person could report both nausea and constipation, so the symptom counts add up to more than 11.

What these numbers are, and are not

They are answers to routine care check-in questions, taken once, at the first eligible follow-up. They are not systematic adverse-event surveillance. Nobody went looking for side effects with a checklist on a schedule. Nobody graded severity. There was no comparison group, so the study cannot say whether the low dose caused fewer side effects than a labeled dose. This article makes no such comparison, and you should be wary of any page that does.

They also come from one point in time. “When do tirzepatide side effects peak?” is a real question, and this study cannot answer it. It has one check-in per person for this analysis, not a week-by-week curve.

When to call a prescriber

At any dose, per the label: severe or lasting stomach pain, with or without vomiting; signs of an allergic reaction; symptoms of low blood sugar if you also take insulin or a sulfonylurea; vomiting or diarrhea that leads to dehydration; a lump or swelling in the neck, trouble swallowing, or hoarseness; vision changes if you have diabetes. Severe symptoms need urgent care. In the PlexusDx program, an independent network of U.S.-licensed clinicians through a state-licensed telehealth platform handles side-effect questions through check-ins.

For weight results from the same study, see microdose tirzepatide results at 3, 7 and 9 weeks. For how the check-in data were handled, see how we checked the data.

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

What side effects did people report on microdose tirzepatide?

At the first eligible check-in in the PlexusDx study, 11 of 58 patients (19.0%) reported any side effect. Nausea was reported by 7 of 58 (12.1%), constipation by 6 of 58 (10.3%), diarrhea by 2 of 58 (3.4%), and vomiting by 0 of 58. Symptoms were not mutually exclusive.

Does a microdose of tirzepatide cause fewer side effects than a full dose?

The PlexusDx study cannot say. It had no full-dose comparison group, and its side-effect data came from routine check-ins, not systematic surveillance. Any claim that a lower dose is gentler needs a study built to test that question. This article makes no such comparison.

When do tirzepatide side effects peak?

The PlexusDx study cannot answer this; it analyzed one check-in per patient, not a week-by-week curve. Per the FDA label, stomach side effects are most common when starting and when the dose goes up. Ask your prescriber what to expect at your dose and schedule.

Why were two patients not counted?

Matched check-in answers existed for 58 of 60 patients. The other 2 had missing or unmatched responses. The study counts them as unknown, not as symptom-free, so no percentage in this article uses 60 as the denominator for side effects. That choice keeps the rates honest.

What tirzepatide side effects need urgent care?

Per the FDA label: severe or persistent stomach pain, signs of allergic reaction, symptoms of low blood sugar with insulin or sulfonylureas, dehydration from vomiting or diarrhea, a neck lump, trouble swallowing, or hoarseness, and vision changes in people with diabetes. Seek urgent care for severe symptoms at any dose.

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.