nausea/vomiting
"I had a couple surgeries on my jaw where I could not open it fully for an extended period of time. I am already semi-allergic to pain meds / anesthesia (excessive vomiting and nausea) so I was terrified to take my pain killers after surgery. The nurse / doctor recommended taking a couple Benadryl tablets (25mg) before the pain meds and it worked wonders! The only side effect is drowsiness."