Lighting a joint. View of a man lighting a cannabis (marijuana) joint with a candle. Superimposed in the foreground is a leaf of the hemp plant (Cannabis sativa). Marijuana consists of the leaves and flowering tops of the hemp plant. The effects of smoking cannabis include mental relaxation, accelerated heart rate, perceived slowing of time and heightened senses. Large doses may result in panicky states, fear of death and illusions. Prolonged use may lead to psychological problems and lung damage.