Meprozine and demerol

I was given Meprozine when Demerol made me vomit. The Meprozine got rid of my terrible headache in 15 minutes and the big side effect was drowsiness. I slept for many hours and felt drowsy for a few hours. It was mellow actually and I am not on any other medication. I didn't have any other noticeable side effects. I thought it worked great and would take it again (just one capsule) if I get a bad headache.

I was prescribed Demerol 50mg. by my physician for extreme pain due to spinal stenosis. My prarmacist instead sold me Mepergan Fortis and told me it is exactly the same thing as Demerol only it has medication to prevent nausea in it. Does anyone out there know if this is true?