This one has a reasonably settled answer, so here it is. Site reactions are usually technique or temperature rather than the material. Injecting straight from the fridge stings more than injecting at room temperature, alcohol that has not dried carries into the puncture and burns, and re-using the same square inch produces the lump people worry about. Rotate genuinely — different quadrant each week, not different spot in the same quadrant.

That is the short version; the long version is somebody else's post.

FDA_TrackerJim said:

Site reactions are usually technique or temperature rather than the material.

Agreed, and site choice does not change absorption for the weekly agents, so rotating costs nothing pharmacologically.

dave_SLC said:

My prescriber wanted a baseline TSH and did not want a calcitonin, and I would like to understand the reasoning rather than just accepting it.

Mine went the same way, slower.

Adding the clinical framing, because it changes how the question reads.

Thyroid cancer screening labs for thyroid monitoring — addressing the boxed warning concern with actual data:

Calcitonin level: 3.0 pg/mL (normal <10). Checked at baseline, month 6, and month 12. Rock stable, no upward trend.

Thyroid ultrasound: normal, no nodules at month 12.

The MTC risk from rodent studies has not been confirmed in human post-marketing data across millions of patient-years. The boxed warning is a regulatory precaution based on animal data. While monitoring is prudent, the clinical risk appears to be negligible.