Phenergan usually is administered orally or through an IV drip.
From the latimes.com
Phenergan has been legal for half a century.
From the washingtonpost.com
More examples
Promethazine: antihistamine (trade name Phenergan) used to treat allergies; also an antiemetic used to treat motion sickness
Promethazine is a first-generation H1 receptor antagonist of the phenothiazine chemical class used medically as an antihistamine antiemetic. It has a strong sedative effect and in some countries is prescribed for insomnia when benzodiazepines are contraindicated. ...
A sedative administered which also controls nausea and vomiting.