I was curious about that myself.

"To slow absorption of injected antigens (e.g., insect stings), a tourniquet may be placed proximal to the injection site. "

https://www.aafp.org/pubs/afp/issues/2003/1001/p1325.html

The article says that tourniquets are no longer recommended. It doesn't seem like a tourniquet would be of any help if you ingested something but reasonable for insect stings. Anyone who has taken a first aid course gets warned multiple times about the danger of leaving a tourniquet on too long but maybe random people aren't aware of it.