It wont hurt you. My little cousin is prescribed it along with Adderall Xr for his disorder. I have had it given to me twice. Once by my own doctor along with valium for an opiate detoxification, and at the hospital along with ativan when I smoked too much glass.
If its only been an hour or two since the H, it will most likely make you a little tired. Actually, it will probably make you feel pretty relaxed.
It is prescribed for alot of things. I know for sure its used off label for some people who are prescribed Adderall. It counteracts some of the effects of amphetamines, or stimulants rather. I also know it is prescribed for insomnia, and pain. Most likely neuropathic pain.
Stay safe