Last reviewed: July 17, 2026
Last updated: July 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.
Medically reviewed by:
Jayden Lee, PharmD, EMBA
Jayden Lee, PharmD, EMBA, is the PlexusDx Medical Science Liaison 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 — science-backed guidance on GLP-1 medications, metabolic health, and precision weight management.
Mounjaro pens deliver tirzepatide, a dual GLP-1 and GIP receptor agonist that has shown significant weight loss results in clinical trials. Each pre-filled pen is engineered to provide exactly four weekly doses, making it convenient for month-long treatment cycles. Knowing how many injections come in each pen helps you plan refills and track your medication supply.
How Many Doses Come in a Mounjaro Pen
Each Mounjaro pen contains four pre-measured doses of tirzepatide. The pen is designed so that you dial your prescribed dose and inject once per week for four weeks before needing a new pen. This fixed four-dose format means most patients require three pens per year if they stay on a stable dose throughout their treatment.
The pen's design includes a dial mechanism that lets you select your specific dose strength, ranging from 2.5 mg up to 15 mg. Once you've injected, the pen automatically resets for the next week's dose. After the fourth injection, the pen is empty and must be replaced with a fresh one.
Why Tirzepatide Injections Use a Weekly Schedule
Weekly tirzepatide injections work because the medication has a long half-life in your bloodstream, allowing steady hormone signaling throughout the seven days between doses. This once-weekly dosing approach improves adherence compared to daily pills, since patients only need to remember one injection per week rather than managing daily medication timing.
Clinical trials supporting tirzepatide's weight loss benefits were conducted using this weekly schedule, which is why healthcare providers recommend sticking to the same day each week. Consistency with your injection timing helps maintain stable appetite suppression and metabolic effects.
Understanding Dose Titration and Pen Supply
Most patients begin tirzepatide at a 2.5 mg starting dose and increase their dose every four weeks under medical supervision. Because dose adjustments happen gradually, you may use different pen strengths as your treatment progresses—your dose may need to go up, but your price won't change at PlexusDx. This titration strategy reduces gastrointestinal side effects while maximizing weight loss results.
PlexusDx compounded tirzepatide injections start at $289/mo (or $249/mo on the 6-month plan) and maintain the same flat price regardless of dose level, making budget planning straightforward as your provider adjusts your therapy upward.
PlexusDx Tirzepatide as an Affordable Alternative
PlexusDx offers compounded tirzepatide injection prepared by licensed 503A compounding pharmacies, providing the same active ingredient at a predictable monthly cost with no insurance requirement. Like brand-name Mounjaro, PlexusDx tirzepatide follows a weekly injection protocol, but patients benefit from transparent flat pricing and HSA/FSA eligibility.
PlexusDx serves all 50 states and can help you understand whether tirzepatide alone or a dual-compound option like GLP-Squared Injection—which combines semaglutide and tirzepatide—might align with your genetic predispositions revealed by the Precision Peptide Genetic Test.
How Your Genetics Relate to GLP-1 Pathways
Not everyone responds to GLP-1 medications the same way. Genetic variants — including GIPR rs1800437, GLP1R rs6923761, FTO rs9939609, and MC4R rs17782313 — relate to the biological pathways these medications act on. These are pathway-level associations only and do not predict how much weight you will lose or how you will respond to any specific medication. PlexusDx maps 14 pathways, 49 peptides, and 150+ genetic insights so you and your provider can see how your genes relate to these pathways. It does not recommend, prescribe, or determine which medication, dose, or peptide is right for you. The PlexusDx Precision Peptide Genetic Test ($99 add-on after your first month of treatment) gives you and your provider pathway-level genetic context to support a more personalized conversation. Genetics is a guide, not a guarantee.
Access Personalized GLP-1 Care Through PlexusDx
PlexusDx offers six prescription GLP-1 protocols to all 50 states — no membership, no insurance required, async intake or live consult. The Tirzepatide Injection starts at $289/mo. Medications are dispensed from licensed 503A compounding pharmacies following strict quality and safety standards. Add a Precision Peptide Genetic Test for $99 to personalize your protocol from day one.
Frequently Asked Questions
Do I need a new Mounjaro pen every month?
Yes, since each pen delivers four weekly injections, you'll need approximately one new pen every month. Most patients use three to four pens annually if they remain on a stable dose throughout their treatment year.
Can I use a Mounjaro pen for more than four injections?
No, the pen mechanism is calibrated to deliver exactly four doses and then empties. Once empty, the pen cannot be refilled and must be discarded safely according to sharps disposal guidelines.
How does PlexusDx tirzepatide pricing compare to Mounjaro?
PlexusDx tirzepatide injections start at $289/mo (or $249/mo on the 6-month plan) with flat pricing across all dose levels, and no insurance or membership fees apply. This transparent model eliminates surprise costs as your provider adjusts your dose upward during treatment.
What genetic factors influence how well tirzepatide works?
The PlexusDx Precision Peptide Genetic Test analyzes variants like GLP1R rs6923761, GIPR rs1800437, and MC4R rs17782313 to reveal how your peptide pathways respond to tirzepatide, helping personalize whether monotherapy or dual-compound GLP-Squared might suit you best.
Are PlexusDx tirzepatide injections FDA-approved?
PlexusDx tirzepatide is compounded by licensed 503A compounding pharmacies and contains the FDA-approved active ingredient tirzepatide, though the compounded form itself is not FDA-approved. Compounding allows affordable access while maintaining quality standards.
Related Reading
Pricing and availability current as of July 2026. Compounded GLP-1 medications are not FDA-approved drug products; they are prepared by licensed compounding pharmacies under federal compounding regulations. Compounded semaglutide and tirzepatide are not the same as Wegovy, Ozempic, Zepbound, or Mounjaro. This article is for informational purposes only and does not constitute medical advice. Consult a licensed healthcare provider before starting, stopping, or changing any medication.
Return to the PlexusDx Education Hub for more evidence-based resources on GLP-1 therapy, metabolic health, and personalized weight management.
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.
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