Complete Guide to GLP-1 Injection Sites:
Rotation and Avoiding Lumps

Proper injection technique is crucial for weight loss medications to be effective. Incorrect injection sites or failing to rotate them not only affects drug absorption but can also cause lipohypertrophy (fatty lumps under the skin), significantly reducing efficacy. This article details the correct injection sites and rotation methods for Mounjaro, Wegovy, and Saxenda.

The 3 Approved Injection Sites

The Importance of Site Rotation

Injecting in the exact same spot every time leads to lipohypertrophy—the formation of hard lumps or nodules under the skin. This thickened fat tissue causes the medication to be absorbed slowly and erratically, leading to fluctuating drug levels in your blood.

Signs of Lipohypertrophy

• Hard lumps or swelling at the injection site.
• Skin looks slightly raised or has a "cottage cheese" texture.
• Injections feel more painful than usual.
• The medication's effectiveness seems to randomly go up and down.

How to Correctly Rotate Sites

Abdominal Rotation (6 Zones)

Thigh Rotation

• Rotate between the left and right outer-mid thighs.
• Keep each new injection at least a finger's width away from the previous one.
• Avoid the inner thigh and areas too close to the knee.

Key Injection Steps

1. Wash your hands thoroughly.
2. For a new pen, take it out of the fridge and let it warm up briefly before first use (cold medicine hurts more). Once opened and in use, pens are stored at room temperature — no warming needed.
3. Disinfect the site with an alcohol swab and let it dry.
4. In Taiwan, all three medications come as multi-dose pens requiring manual injection. Insert the needle at a 90-degree angle into subcutaneous tissue.
5. After injection, hold for a few seconds as directed by the product label before removing.
6. Apply light pressure, but do not massage the injection site (massaging accelerates absorption and can increase side effects).

Common Mistakes

• ❌ Injecting too deep into the muscle (hurts more, absorbs differently).
• ❌ Pulling the needle out too quickly (medicine leaks out).
• ❌ Hitting the exact same spot every time (causes lumps).
• ❌ Injecting immediately after taking it out of the fridge (causes stinging).
• ❌ Rubbing or massaging the site after injection.

Storage Guidelines

• Unused pens: Keep refrigerated at 2–8°C (36–46°F). Never freeze.
• After removing from fridge (unused): Can be kept at room temperature (below 30°C / 86°F) for up to 21 days (for Mounjaro; check specific times for others).
• Keep away from direct sunlight and high heat.
• Always use a fresh needle for every injection (if using multi-dose pens like Saxenda).

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