THC-Varin (stupid autocorrect on my phone from prior post) (AKA THC-V)is a highly-psychoative, hard-hitting THC homologue that is highly stimulating with very short duration of effect. High levels of this are present in African and Asian sativa strains. If you've ever taken a hit of stuff that got you high immediately, chances are you just had a quick THC-V dose from the strain. It lasts about 15 minutes, then fades away, leaving the normal delta-9 THC to do its thing for the next few hours.

Vivarin is brand of caffeine pill (haven't heard the name since the Nineties), I've not heard of combining it with THC.