THE FAILURE OF THE PILOT-IN-COMMAND TO MAINTAIN ADEQUATE ROTOR RPM DURING A PRECAUTIONARY LANDING FOLLOWING THE LOSS OF ENGINE OIL. IN ADDITION, THE PILOT FAILED TO INSURE THAT THE ENGINE CONTAINED ADEQUATE OIL, AND THAT THE OIL DIP STICK WAS SECURE PRIOR TO TAKEOFF. A FACTOR WHICH CONTRIBUTED TO THE ACCIDENT WAS THE PILOT'S IMPAIRMENT DUE TO MARIJUANA.