Mounjaro 'best site' claims on TikTok: what the data says

What did @my.journey.with.marc actually say?

Mark claimed that switching his tirzepatide injection to his thigh gave him more consistent cravings control and less of the "up and down feeling" week to week. He was clear this was personal experience, not a rule, and he actively discouraged copying him without understanding why. He also told viewers to test sites and pay attention to how they feel, which is genuinely decent advice that a lot of creators skip over.

He framed this around a 57-kilogram weight loss on tirzepatide and presented himself as someone now in maintenance. He didn't claim the thigh works for everyone, and he didn't prescribe a dose or protocol. That restraint matters and is worth noting upfront before we get into what the evidence actually says.

Does the science back this up?

Partially, yes. The idea that injection site affects drug absorption is not invented, but the evidence is messier than most people realise, and tirzepatide-specific data is thin.

A 2014 review by Heise et al. in Diabetes Technology and Therapeutics found meaningful differences in insulin absorption rates between abdomen, thigh, and arm sites, with the abdomen generally showing faster uptake. For GLP-1 receptor agonists, the picture is less clear. A 2022 pharmacokinetic analysis of semaglutide in Diabetes, Obesity and Metabolism found no statistically significant difference in peak plasma concentration between subcutaneous sites in a controlled setting. However, real-world variables like tissue composition, lipohypertrophy from repeated injections, and individual body fat distribution can all shift absorption in ways a controlled trial won't capture.

Mark's reported subjective experience of steadier cravings from thigh injection is biologically plausible if he had developed lipohypertrophy at his abdominal sites from months of injections to the same area. Injecting into hardened tissue genuinely does blunt absorption. So his switch may have fixed that problem rather than the thigh being inherently superior.

What did they get wrong (or right)?

Mark got the core message right. He was right that injection sites can behave differently for different people. He was right that copying someone else's site without testing your own response is not a good strategy. And he was right to say this is about his body, not a universal rule.

What he didn't address, and this is the real gap in the video, is lipohypertrophy. This is the most clinically important reason to rotate sites and it goes completely unmentioned. If viewers hear "try the thigh" and then inject the same thigh spot every week, they have learned nothing useful. The lesson isn't which site, it's that rotation within and across sites matters enormously for consistent absorption.

He also used the word "cravings" in a way that conflates multiple mechanisms. Tirzepatide's appetite effects come from GIP and GLP-1 receptor dual agonism centrally and peripherally. Whether a subcutaneous depot in the thigh versus abdomen meaningfully alters that signalling over a weekly dosing window is not something the current evidence supports as a firm conclusion. His experience is real. The mechanistic explanation he implies is speculative.

What should you actually know?

Injection site rotation is not optional, it is a basic clinical requirement for any injectable medication given subcutaneously long-term. The American Diabetes Association recommends rotating within a region and across regions to prevent lipohypertrophy, a condition where fatty lumps form under the skin and can reduce drug absorption by up to 25 percent according to a 2016 study by Blanco et al. in Diabetes Care.

The approved sites for tirzepatide per the Zepbound and Mounjaro prescribing information are the abdomen, thigh, and upper arm. No site is listed as superior. Your prescriber or pharmacist is the right person to help you troubleshoot absorption issues, not a TikTok comment section.

If you feel like your medication stopped working or your week-to-week response is unpredictable, lipohypertrophy is one of the first things worth discussing with your provider, not just which site you use. Mark's instinct to switch and pay attention was correct. The explanation for why it helped him is more complicated than the video suggests.