Kevod Harav. When one has to inject during Shabbat pain killers or insulin, does one have to be careful not to inject into a vein?

Horav Shlomo Miller’s Shlit’a opinion is that indeed one should be careful and avoid injecting directly into a vein or artery when not required, as drawing blood from them into the syringe may be a Biblical prohibition. The needle should go into muscle or other tissue when medically also recommended.