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GLP-1 AgonistNot WADA ProhibitedCompare

Tirzepatide

Also known as: Mounjaro, Zepbound, LY3298176

3
1 · Natty510 · Enhanced

Lower numbers = closer to natural. Higher numbers = more enhanced.

Why this rating?

Per NEJM's SURMOUNT-1 trial, tirzepatide produces up to ~21% body weight loss (intention-to-treat) at the 15mg dose through dual GLP-1/GIP receptor activation, mimicking natural incretin hormones. Roughly 75% of weight lost is fat and 25% is lean mass, but a 2025 DXA sub-study of SURMOUNT-1 (Look et al., Diabetes Obes Metab) found this ratio was essentially identical in the placebo (diet-only) arm, so tirzepatide does not spare muscle any better than dieting alone. FDA-approved for diabetes and weight management. Does not affect anabolic hormones or athletic performance. Rated 3 as a prescription medication working through natural hormonal appetite/satiety pathways, in line with the other GLP-1 agents on this list.

Overview

A first-in-class dual GLP-1/GIP receptor agonist (sometimes called a "twincretin"). This 39-amino acid synthetic peptide activates both incretin receptors, producing superior weight loss and glycemic control compared to GLP-1-only agonists like semaglutide. The most effective FDA-approved pharmaceutical weight loss agent currently on the market (investigational triple agonists like retatrutide show larger effects in trials but are not yet approved).

Important Warnings

  • •BLACK BOX WARNING: Risk of thyroid C-cell tumors (observed in rodents at clinically relevant doses). Unknown if occurs in humans.
  • •Contraindicated with personal or family history of medullary thyroid carcinoma (MTC)
  • •Contraindicated with Multiple Endocrine Neoplasia syndrome type 2 (MEN 2)
  • •May affect absorption of oral medications due to delayed gastric emptying
  • •Not studied in patients with history of pancreatitis
  • •Can cause acute kidney injury through dehydration from GI side effects
  • •Diabetic retinopathy complications reported in patients with existing retinopathy
  • •Weight regain typically occurs after discontinuation

Purpose & Use Cases

Weight Loss

Produces up to ~21% body weight loss (intention-to-treat) at the 15mg dose in SURMOUNT-1, one of the largest effects of any approved pharmaceutical intervention. Among participants who stayed on treatment throughout the trial, average weight loss reached ~22.5% (52 lbs) at the highest dose.

Type 2 Diabetes Management

Provides superior glycemic control with significant HbA1c reductions; patients who lose substantial weight can see blood sugar return to normal (remission) without medication.

Metabolic Health

Improves multiple metabolic markers including lipids, blood pressure, and inflammatory markers.

Body Recomposition

Primarily a fat loss agent: roughly 75% of weight lost is fat and 25% is lean mass. A 2025 DXA sub-study of SURMOUNT-1 found this ratio was essentially the same in the diet-only placebo arm, so tirzepatide does not spare muscle better than dieting alone; it simply causes more total weight (and more total muscle) to be lost.

Benefits

  • Most effective FDA-approved weight loss medication available (up to ~21% body weight reduction, intention-to-treat, at the 15mg dose)
  • Superior to semaglutide in head-to-head trials (SURMOUNT-5: 20.2% vs 13.7% weight loss at week 72, a ~6.5 percentage-point difference)
  • Significant improvements in insulin sensitivity and glycemic control
  • Non-inferior to dulaglutide (another GLP-1 drug) for major cardiovascular events in the SURPASS-CVOT trial, with a favorable trend that did not reach statistical superiority
  • Once-weekly dosing for convenience
  • Can push HbA1c into the normal range (diabetes remission) in some patients who achieve large weight loss
  • Improvements in blood pressure and lipid profiles
  • FDA-approved for obstructive sleep apnea (2024)

Good to Know

A dual GLP-1/GIP "twincretin": more effective than semaglutide

Tirzepatide hits two incretin receptors (GLP-1 and GIP), producing up to ~21% body-weight loss (ITT, 15mg) in SURMOUNT-1 and beating semaglutide head-to-head in SURMOUNT-5 (20.2% vs 13.7% at week 72). It is currently the most effective FDA-approved pharmaceutical weight-loss agent.

Same fat-to-lean ratio as dieting: muscle loss is still real

Tirzepatide loses roughly 75% fat to 25% lean mass. A 2025 DXA sub-study of SURMOUNT-1 found the diet-only placebo arm lost weight in almost the identical ratio, so tirzepatide does not spare muscle any better than dieting alone; it just produces a bigger total loss (fat and muscle both). Resistance training and high protein remain necessary to hold muscle, exactly as with any GLP-1.

The weight rebounds if you stop: plan the off-ramp

SURMOUNT-4 showed substantial regain after switching to placebo. Like the other GLP-1s, tirzepatide is best viewed as long-term therapy or a slow, habit-building taper, stopping abruptly reverses much of the loss.

Not anabolic, not WADA-banned: muscle protection is on you

It works through satiety and glucose control, not any performance pathway, and is not on the Prohibited List. It is an effective cutting aid but builds nothing. Training and protein do the muscle-preserving work.

Dosage Guidelines

Experience LevelDosage Range
Beginner2.5 – 5 mg/week
Intermediate5 – 10 mg/week
Advanced10 – 15 mg/week
Frequency
Once weekly subcutaneous injection
Typical Cycle Length
12 – 52 weeks
Notes

Start at 2.5mg weekly for 4 weeks (initiation dose, not therapeutic). Increase by 2.5mg every 4+ weeks based on tolerability. Maximum dose is 15mg weekly. Available strengths: 2.5, 5, 7.5, 10, 12.5, 15mg.

Side Effects

Nausea

common
Severity
2/5

Most common side effect. Affects ~25-29% of users (vs ~8% placebo) in the Zepbound weight-management trials and ~12-18% in the Mounjaro diabetes trials, generally dose-dependent. Usually mild to moderate and decreases over time.

Mitigation

Slow dose titration, eat smaller meals, avoid fatty foods. Usually improves after first few weeks.

Diarrhea

common
Severity
2/5

Affects approximately 19-23% of users in weight-management trials (12-17% in diabetes trials), dose-dependent.

Mitigation

Usually transient. Stay hydrated. May need to slow titration.

Vomiting

uncommon
Severity
2.5/5

Affects approximately 8-13% of users in weight-management trials (5-9% in diabetes trials), dose-dependent.

Mitigation

Slow titration, smaller meals, avoid trigger foods.

Constipation

uncommon
Severity
1.5/5

Affects approximately 6-17% of users due to slowed gastric emptying. In the Zepbound weight-management trials rates were, unusually, highest at the lowest dose (17% at 5mg vs 11% at 15mg).

Mitigation

Increase fiber and water intake. May need stool softeners.

Hypoglycemia

uncommon
Severity
3/5

Risk is low when used alone (glucose-dependent mechanism) but increases significantly when combined with insulin or sulfonylureas (up to 14-19%).

Mitigation

Reduce doses of concurrent insulin or sulfonylureas. Monitor blood glucose.

Injection Site Reactions

uncommon
Severity
1/5

Affects approximately 6-8% of users in weight-management trials (vs 2% placebo); 1-4.5% in diabetes trials. Includes erythema, pruritus, swelling.

Mitigation

Rotate injection sites between abdomen, thigh, and upper arm.

Increased Heart Rate

common
Severity
2/5

Mean increase of 1-4 bpm across trials (1-3 bpm in weight-management trials, 2-4 bpm in diabetes trials). Sinus tachycardia (a rise of 15+ bpm) reported in roughly 4-10% of patients in diabetes trials.

Mitigation

Usually not clinically significant. Monitor if symptomatic.

Acute Pancreatitis

rare
Severity
5/5

Rare but serious. Incidence approximately 0.2% (0.23 per 100 patient-years).

Mitigation

Discontinue immediately if suspected. Not studied in patients with history of pancreatitis.

Gallbladder Disease

rare
Severity
3/5

Cholecystitis and cholelithiasis reported at rates higher than placebo (up to 0.6%).

Mitigation

Monitor for symptoms. Rapid weight loss increases gallstone risk.

General Mitigation Strategies

GI side effects are dose-dependent and usually improve with continued use. Slow titration is key - do not rush dose increases. Stay well hydrated. Discontinue and seek medical attention for severe abdominal pain (pancreatitis concern). In pooled Zepbound weight-management trials, GI adverse events occurred in ~56% of tirzepatide-treated patients across all doses (5/10/15mg) vs 30% with placebo.

Support Supplements

Ancillary supplements commonly run alongside Tirzepatide to manage side effects, support the target tissue, or fill nutrient demands it creates.

High protein intake

Key

Roughly a quarter of the weight lost on tirzepatide is lean mass, and appetite suppression makes protein the intake most likely to fall short. A high protein target is the main lever protecting muscle during the cut.

Dose
1.2-2.0 g/kg bodyweight per day
Timing
Spread across meals; shakes help when appetite is low

Resistance training

Key

About 25% of weight lost on tirzepatide is lean mass (the same ratio seen with diet alone). Lean tissue is lost without a resistance stimulus. Training plus protein pushes the ratio further toward fat.

Dose
2-4 sessions/week
Timing
Throughout the loss phase

Creatine monohydrate

Supports strength and lean-mass retention during weight loss; cheap and well-evidenced.

Dose
3-5g/day
Timing
Daily

Fiber + hydration (and electrolytes)

Delayed gastric emptying and reduced intake commonly cause constipation and dehydration; fiber, fluids and electrolytes address the main GI complaints and reduce kidney-injury risk from GI fluid loss.

Dose
Adequate fiber; deliberate fluid/electrolyte intake
Timing
Daily

Post Cycle Therapy (PCT)

✓PCT Not Required

Not hormone-based. No PCT required. However, weight regain is common after discontinuation - lifestyle modifications should be maintained.

How It Works

Tirzepatide is an "imbalanced" dual agonist with high affinity for GIP receptors (comparable to native GIP) and approximately 5x weaker affinity for GLP-1 receptors than native GLP-1. It stimulates glucose-dependent insulin secretion, suppresses glucagon, reduces appetite through central nervous system effects, improves insulin sensitivity, and produces approximately 75% fat mass loss vs 25% lean mass loss during weight reduction.

Fundamentals

Reference on the practices relevant to Tirzepatide: how they are done and where they go wrong. Not a recommendation to use it.

Reconstitution & concentration math→

Turning this powder into a measured dose

Sterile technique & injection-site infection→

Avoiding abscesses and cellulitis

Bloodwork: what to measure and when→

The markers that matter here

Warning signs & when to seek care→

When to stop and get help

WADA Status

✓Not Prohibited by WADA

Tirzepatide (Mounjaro/Zepbound) is not currently listed on the WADA Prohibited List. It is an FDA-approved prescription medication for diabetes and weight management.

References

Last updated: July 18, 2026