An aphrodisiac is a substance alleged to increase libido, sexual desire, sexual attraction, sexual pleasure, or sexual behavior. These substances range from a variety of plants, spices and foods to synthetic chemicals. Natural aphrodisiacs like cannabis or cocaine are classified into plant-based and non-plant-based substances. Synthetic aphrodisiacs include MDMA and methamphetamine. Aphrodisiacs can be classified by their type of effects. Aphrodisiacs that contain hallucinogenic properties like bufotenin have psychological effects on a person that can increase sexual desire and sexual pleasure. Aphrodisiacs that have smooth muscle relaxing properties like yohimbine have physiological effects on a person that can affect hormone levels and increase blood flow.