Are GLP-1 App Medication Charts Reliable?

Expert insights on why pharmacokinetics aren’t as simple as the lines on your screen.

Author

Lucas Veritas
September 18, 2025

Most GLP-1 tracking apps like Shotsy or Glapp feature estimated drug concentration charts, offering users a visual sense of how medication levels fluctuate in your body after injection.

For many, these graphs provide a sense of structure, helping to align perceived effects like hunger suppression or side effects with the expected pharmacokinetics.

However, these visualizations vary across platforms. When I reviewed several level charts, I noticed each presented slightly different data, including discrepancies in time-to-peak concentration and duration of therapeutic effect.

So which apps are giving you more accurate information?

This question matters more than you might think. When you're trying to understand your body's response to these medications, unreliable data can lead to unnecessary worry or poor timing decisions around titration or side effect management.

Apps developers claim to base their estimates on published research about how GLP-1 medications behave in the average person's body. They take data points like when the medication reaches peak concentration and how quickly it's eliminated, then create visual models.

Expert Analysis: "Don’t Waste Your Money"

To dig deeper into this issue, I've invited Dr. Joseph Bertino, a clinical pharmacologist who specializes in how medications move through the body.

Dr. Bertino has served on FDA advisory committees and also happens to use tirzepatide himself -giving him both the scientific expertise and personal experience to evaluate these apps critically.

Dr. Bertino: “You may find it fun to plot concentration but it’s fun only and scientifically inaccurate”.

The websites and apps that plot serum concentrations are inaccurate because of the variation in blood concentrations and the time to peak. In the original studies the time to peak ranged from 8-72 hours, so using a fixed time to peak introduces inaccuracies.

Someone who says "when my serum concentrations are low my appetite suppression is gone" well for sure, at the end of the dosing interval you may feel less effect, you don't need to make an inaccurate plot to know that, it's just sensible, it’s pharmacodynamics.

Medication Levels in Shotsy app

The Eli Lilly (the company that sells Zepbound/Mounjaro) showed no difference in pharmacokinetics based on total body weight. There is some minor difference but no clinical differences have been shown in terms of efficacy. The same is true for sex, kidney disease and liver disease.

Tirzepatide is approximately 99% protein bound, and protein bound drug is NOT active drug. So only 1% of the drug is not bound to protein, and that is the active drug. This gives the drug a long half-life (time it takes to reduce blood concentration by 50%).

Highly protein bound drugs have small body volumes (volume of distribution) that the drug resides in. For tirzepatide, the average is 10 liters, which is only 2 times the average of total blood in an adult. This is very different from some drugs which have volumes of distribution of hundreds of liters.

In terms of concentrations in the blood, there is a 2-3 fold variation in the concentration of the drug in the blood with the same dose in people. However, the drug is still effective in many people despite this variation in blood concentration. We know that women lose weight faster than men, but this does not appear to be due to different pharmacokinetics. No clear relationship of concentration to effect has been shown.

Why do people lose weight with a large variation in exposure?

This probably has to do with sensitivity or lack of sensitivity of the receptors that the drug binds to. This may be due to genetics (you can't pick your parents), but currently this is speculation - we need to have more data.

Some people are very sensitive to the drug and lose a good amount of weight at small weekly doses. Others don't lose a lot of weight at maximum doses. But this does not appear to be due to differences in drug pharmacokinetics. (The 2.5 mg dose was used to get the body "used" to the drug, but turns out some people lose weight at that dose.)

Remember these drugs are agonists. That is, they mimic the effect of the naturally occurring proteins that the body makes. The drug binds to these receptors in the body but stays on the receptor longer to give the good and negative effects we see with tirzepatide.

Comments from GLP-1 tracking apps

I also reached out directly to the teams behind several popular GLP1 tracking apps. While most apps include broad disclaimers explaining they use "mathematical models based on peer-reviewed studies", I asked for the specifics behind their calculations.

  • Shotsy: No response to my inquiry, but user reports suggest they use a simplified formula assuming peak concentration at 24 hours with 80% bioavailability

  • GLP-1 Plotter: Also didn't respond, with users reporting similar simplified calculations to Shotsy

  • Artem from Glapp: Each person clears the drug differently, with unique peaks and valleys. Without actual concentration testing it is impossible to map an individual’s precise PK curve. That’s why all current apps usually show an average person profile. At Glapp we balance pharmacokinetic accuracy with the need to keep information understandable for non-expert users. We are working with pharmacologists to implement the models as used by Lilly and Novo Nordisk. Our approach is to gradually improve accuracy, for example, this month we will begun factoring in individual characteristics to provide a more tailored GLP-1 level chart.

    Glapp visualizes the drug cycle after each shot

 

  • Marvin from GLPeak: We aim to provide both accuracy and accessibility by offering two ways to view medication levels. Our app includes a full pharmacokinetic model based on published parameters such as absorption rate, bioavailability, and elimination half-life. This ensures the science is grounded in established data. At the same time, many people are used to seeing simplified “step-style” graphs. We included this style because it makes it easy to see how doses accumulate and decline week to week. For those who want more precision, our pharmacokinetic toggle is available.

GLP-1 tracking apps can be valuable tools for monitoring injections, logging symptoms and staying consistent with your therapy plan. However, it's crucial to approach their medication level charts with a healthy dose of skepticism.

While developers aim to improve their models, the significant individual variations in drug metabolism mean these estimated medication levels charts will likely remain educated guesses rather than precise reflections of your internal state.

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Lucas Veritas 

 

 

I’m a true GLP-1 believer.

Tirzepatide (Mounjaro) user and patient advocate.

I lost 100+ lbs, found my energy and gained a new mission: helping others succeed with healthy weight loss on GLP-1s

Disclaimer: This article reflects my personal experience and independent research. It is not a substitute for professional medical advice. Always consult a qualified healthcare provider before making decisions about your health or treatment plan.

Scientific References for this article:

Tirzepatide - Khashayar Farzam; Preeti Patel, 2024

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