GLP-1 injection site safety: what TikTok gets right and wrong

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

Mark's core message is straightforward: stick to the injection sites listed in the official prescribing guidance for Mounjaro and Wegovy, and ignore anyone on social media telling you to inject elsewhere. He's specifically alarmed by advice he's seen pointing people toward areas with "major blood flow," which he flags as dangerous. He's transparent that he's not medically qualified himself, but argues his information comes from manufacturer guidance and conversations with clinical experts on his podcast. He also calls out a conflict of interest worth noting: some creators spreading this advice are paid affiliates, a category he includes himself in for other products.

His central position is not complicated. The approved subcutaneous injection sites for tirzepatide (Mounjaro) and semaglutide (Wegovy) are the abdomen, thigh, and upper arm. He's not adding nuance or edge cases. He's saying follow the label.

Does the science back this up?

Yes, on the core point. The approved sites are correct, and there are real pharmacokinetic reasons for this, not just regulatory box-ticking.

Subcutaneous absorption of GLP-1 receptor agonists varies by injection site. A study by Heise et al. (2014, Diabetes, Obesity and Metabolism) found that subcutaneous absorption kinetics differ meaningfully depending on tissue depth, vascularity, and local blood flow. Injecting into highly vascularized tissue or accidentally hitting intramuscular tissue can alter absorption rates and increase the risk of adverse effects. The prescribing information for tirzepatide (Eli Lilly, 2023) and semaglutide (Novo Nordisk, 2021) both explicitly limit injection to abdomen, thigh, and upper arm, and specify avoiding areas with broken skin, bruising, or active lipodystrophy. There's no published clinical trial supporting alternative injection sites for either drug. The warning about areas with major blood flow is clinically grounded. Accidental intravascular injection, while rare with standard technique, is a known risk with any injectable medication. Mark isn't overstating the danger here.

What did they get wrong (or right)?

He got the main thing right. The approved sites are what the evidence supports, and the concern about unapproved sites is legitimate. But a few points deserve scrutiny.

Mark says he's seen people told to inject into "areas with major blood flow" without specifying what areas he means. That vagueness matters. Some creators discussing things like the upper arm or deltoid region are not necessarily wrong depending on the specific guidance, since the upper arm is an approved site for both drugs. If his objection is about truly off-label areas, he should name them. The lack of specificity makes it harder to evaluate whether what he saw was actually dangerous or just unfamiliar to him. His self-disclosure is a genuine positive. Saying "I'm not medically qualified" upfront and pointing people to official documentation is the right approach. He also correctly identifies the affiliate incentive problem, which is a real issue in the GLP-1 content ecosystem. However, his 126-pound weight loss claim over under a year is presented without context. That rate is well above average for tirzepatide trials (SURMOUNT-1 showed roughly 20-22% body weight reduction over 72 weeks for the highest dose cohort). It's not impossible, but presenting it without caveats could set unrealistic expectations.

What should you actually know?

The approved injection sites for both Mounjaro and Wegovy are the abdomen, upper thigh, and upper arm. These are not arbitrary. The subcutaneous fat in these regions provides consistent absorption profiles and reduces the risk of intramuscular injection or accidental vascular involvement. Rotating within these sites, not just between them, also matters. Repeated injection at the same spot can cause lipohypertrophy, a buildup of fatty tissue that impairs drug absorption. This is well-documented in insulin literature (Blanco et al., 2013, Diabetes Care) and applies to GLP-1 injectables by the same mechanism.

If you are seeing advice online to inject into your neck, groin, chest, or any other unlisted area, that is not a hack. It is an unvalidated practice with no clinical safety data behind it. Your prescriber or pharmacist is the right source for injection technique questions, not a TikTok comment section. Mark is right that this is a prescription medication. The appropriate thing to do with injection site uncertainty is call your pharmacy, not scroll for answers.

• Always follow the site-specific instructions in your medication leaflet.
• Rotate injection sites within each approved region to prevent lipohypertrophy.
• Report any unusual swelling, pain, or skin changes at injection sites to your prescriber.