nausea/vomiting
"I got a severe back injury about 2 years ago.  Couldn't function pain was so bad.  So my doctor started putting me on codiene, then vicoden, then tramadol, and then so on but they all gave me hours of vomiting, gut wrenching cramps, and sweating.  Read about benadryl being used to prevent this side effect.  I took 3 25 mg tabs.  I know that is one over recommended but I was desperate.  35 mins later I was sitting with my kids and not the trash can for the first time in a while.  I can't believe I didn't figure this out sooner especially with a biotech degree."