The failure of the pilot to maintain airspeed and inadvertent stall of the airplane by the pilot-in-command resulting in the uncontrolled descent and in-flight collision with a house. Contributing factors in the accident were the loss of engine power due to undetermined reasons, the operation of the airplane by the pilot-in-command under the influence of marijuana contrary to federal regulations, and the unsuitable terrain encountered after takeoff. A finding in the investigation was the operation of the airplane by the pilot-in-command contrary to federal regulations for his use of antidepressant medication which he was warned against.