Microdosing GLP-1: Lower Doses for Endurance Athletes

Thomas Prommer Hybrid Athlete & Technology Executive Follow on Strava

Published: March 27, 2026

Updated: April 9, 2026

What Is GLP-1 Microdosing?

Microdosing GLP-1 means using semaglutide or tirzepatide at doses significantly below the standard therapeutic targets. For semaglutide, this typically means staying at 0.25mg or 0.5mg weekly rather than titrating up to the FDA-approved weight management dose of 2.4mg.

The concept has gained traction among endurance athletes for a practical reason: standard doses suppress appetite so aggressively that many athletes cannot consume enough calories to fuel training. When you are running 80-100km per week or training 12+ hours for an Ironman, eating enough is already a challenge. A medication that makes food repulsive can turn a training stimulus problem into a fueling crisis.

The idea is simple — take enough to nudge body composition in the right direction, but not so much that you cannot eat when you need to perform.

The Athlete's Dilemma

The core tension is this: GLP-1 medications work partly by reducing appetite and slowing gastric emptying. Both of those mechanisms are helpful for the average patient trying to eat less. Both are potentially harmful for an endurance athlete who needs to consume 60-90g of carbohydrates per hour during a marathon or Ironman.

At standard doses, many athletes report:

• Inability to consume gels or solid food during long sessions without nausea
• Feeling full after half a meal, making it difficult to hit daily calorie and protein targets
• GI distress during high-intensity efforts, particularly in the heat
• Bonking during long runs because the body is not absorbing carbohydrates fast enough

These are not minor inconveniences. For a marathoner, failing to fuel properly means hitting the wall at 30km. For a triathlete, it can mean a DNF. The medication is working exactly as designed — it is just designed for sedentary patients, not athletes burning 3,000-5,000 calories in a single session.

Standard Dosing vs. Microdosing Comparison

Benefits for Endurance Athletes

Preserved fueling ability

The most important benefit for athletes: at 0.25-0.5mg, most people can still eat a full meal and tolerate race nutrition products. You might eat slightly less than usual, but you will not be staring at a plate of pasta feeling physically unable to take another bite.

Fewer GI issues during training

GI distress is the most common reason athletes discontinue GLP-1 medications. Lower doses produce significantly less nausea, and the delayed gastric emptying effect is milder. For athletes whose training depends on mid-session fueling, this is the difference between a medication that helps and one that sabotages.

Lower cost

If you are using compounded semaglutide (where you control the dose precisely), a lower weekly dose means your supply lasts longer. At 0.25mg weekly versus 2.4mg, you are using roughly 10% of the standard dose. Even with brand-name pens, staying at lower titration levels means fewer refills.

Potentially better lean mass preservation

Slower weight loss, in general, leads to a better ratio of fat loss to lean mass loss. When you combine a lower dose with resistance training and high protein intake, you can tilt the body composition equation more favorably than rapid weight loss at a standard dose.

Risks and Unknowns

Intellectual honesty requires acknowledging what we do not know:

• Less studied: Clinical trials tested specific doses (0.25mg for 4 weeks, then up). Sustained low-dose use for body composition in athletes is not well-characterized in research.
• May be less effective: Dose-response curves exist for a reason. Some athletes may find that 0.25mg does not move the needle enough to justify the cost and commitment.
• Off-label territory: Using GLP-1 at doses below the therapeutic target for an unlicensed indication (athletic body composition) means your physician is operating outside established guidelines.
• Individual variation: GLP-1 receptor sensitivity varies between individuals. What works at 0.25mg for one person may require 0.5mg or more for another.
• Long-term unknowns: We do not have safety data for decades of low-dose GLP-1 use in otherwise healthy, lean athletes. The risk profile is likely favorable, but "likely" is not "proven."

My Approach

My entire GLP-1 protocol is effectively a microdosing case study. I was prescribed Mounjaro (tirzepatide) 5 mg KwikPen and used half the pen per injection — 2.5 mg per week. This is the lowest available tirzepatide dose. The standard titration protocol starts at 2.5 mg and escalates through 5 mg, 7.5 mg, 10 mg, 12.5 mg, up to 15 mg. I stayed at the floor.

The decision was deliberate. My goals were modest: break the hunger cycle, lose 3-5 kg over 5 weeks, and stop. Not dramatic weight loss. Not a long-term protocol. I needed just enough pharmaceutical support to shift the trajectory, not to suppress my appetite into the ground.

The result: 94.5 kg down to approximately 90 kg measurement weight in 5 weeks on the minimum dose. Body fat estimate dropped from 13.0% to 11.3% (circumference-based). Waist and belly circumferences decreased by 2-3.5 cm. Those numbers were achieved on a dose that most titration protocols treat as the on-ramp before the "real" dose.

The plan from the start was to taper and stop after 5 weeks (ending around March 27). This was never meant to be an indefinite protocol. Five weeks, minimum effective dose, achieve the modest goal, get off.

Why microdosing made sense for me specifically

As an endurance athlete in the middle of Ironman preparation, I need to be able to eat. Full appetite suppression at a higher dose would directly impair my ability to fuel 4-6 hour training sessions. On the bike, I consume 100+ grams of carbohydrates per hour. On long runs, I need gels and fluids that absorb without GI distress. A standard therapeutic dose — designed to make sedentary patients eat dramatically less — would have turned every long session into a fueling crisis.

At 2.5 mg tirzepatide, the appetite suppression was precise enough to do what I needed: reduce cravings and emotional eating between meals, make it easier to maintain a modest caloric deficit, and break the snacking habits that had kept me 3-5 kg above my target weight. But during training, when I needed to eat, I could eat. The fueling worked. 100+ grams of carbs per hour on the bike with no issues. That balance — suppression when I did not need calories, normal appetite when I did — is why microdosing suited my situation.

The appetite suppression pattern had a rhythm: strong effect on days 1-5 post-injection, then a gradual return of hunger on days 6-7 before the next dose. Those last two days were the window where discipline mattered. The medication handled the easy days; I had to handle the hard ones.

Going lower: 20 units (April 2026 update)

After 6 weeks at 30 units (2.5mg), I wanted to know: can I get away with less? I dropped to 20 units, roughly 1.67mg per week. If 2.5mg was already a microdose, maybe an even smaller amount would still handle the cravings while using less medication.

It sort of works, but the end of the week falls apart. Days 1-5 post-injection still feel controlled. But at 30 units, days 6-7 were uncomfortable but manageable — hunger came back, but without the compulsive edge. At 20 units, the cravings on days 6-7 hit with real force. I had binging episodes I had not had since before starting GLP-1.

I also delayed my injection by two days the week of April 8, which made things worse. The usual 1-2 day gap before the next dose became nearly 4 days, and that was enough for the old patterns to fully reassert themselves. If you are going to reduce the dose, you cannot afford to be sloppy with timing. There is less room for error.

Weight went from 89.0kg at peak effect (30 units, late March) to 91.96kg on April 8. Normal fluctuation accounts for some of that, but the binges are a real part of it. Clinical trials at standard doses would never show this — nobody is studying what happens when an athlete tries to dial a microdose even lower. The craving control drops off faster than you would expect from the dose change alone.

Who Should Consider Microdosing

Microdosing GLP-1 is not for everyone. Based on my experience and conversations with other athletes, here is a decision framework:

Microdosing may be right if you:

• Only need to lose 3-8kg to reach your target race weight
• Train at high volume (10+ hours/week) and cannot afford to compromise fueling
• Have a history of GI sensitivity during exercise
• Are preparing for a specific race and cannot risk GI disruption
• Want to use GLP-1 as a tool alongside an already-disciplined nutrition plan

Standard dosing may be more appropriate if you:

• Have significant weight to lose (15kg+) and are not currently in peak training
• Are in an off-season or base-building phase with lower fueling demands
• Have tried microdosing without meaningful results after 8-12 weeks
• Have metabolic health concerns (pre-diabetes, insulin resistance) that require therapeutic doses

The key principle: find the minimum effective dose for your situation. Start low, give it 6-8 weeks, and only increase if the results are not materializing. Your physician should be involved in every dose decision.

For the full context behind my microdosing approach — including weight timeline, body composition changes, and race data — see my complete GLP-1 journey. For the science behind why I chose tirzepatide over semaglutide, see the tirzepatide vs semaglutide comparison.