False. The purpose of the birth control pill is to control birth, not to regulate cycles. Cycle regulation is a side effect. The inhospitable endometrium is main effect (as well as preventing ovulation, and changing the viscosity of cervical mucus).
BS. The purpose of the "birth control" pill is whatever a physician prescribes it for. If researchers discovered tomorrow that it was also effective against allergies, then not only would doctors prescribe it for that purpose, but the drug companies would seek FDA approval to advertise it for that purpose.