To sterilize him. After all he does still have testicles.I can't think of any other reason they would have given it to him?
Whelp, time for the Dirty Needle Diseases Saga.
It gets injected into the butt muscle normally.How long until he throws it down a storm drain during an autistic tantrum?
Possibly when he can't find a vein under the thick layers of blubber on his fat arms.
A lot of the troons we follow are on injectable estrogen. It's not that unusual for MtF. They waffle endlessly about how they get "PMS" in the lead up to their next injection being due.