Cocaine is both a central nervous system stimulant and a topical anaesthetic. It is found in the leaves of the Erthroxylum coca plant. The traditional method of coca use is to "chew" the leaves (the leaves are actually not chewed so much as sucked, producing a mild stimulation. Outside of South America it is generally used in its more refined and extracted forms: either powder cocaine, or freebase cocaine which produce much stronger effects than "chewing" the leaves. The term "Crack" is alternately used to refer to street quality freebase cocaine, or to refer to the product of a particular manufacturing process which uses sodium bicarbonate rather than a flammable solvent. Powdered cocaine is generally insufflated (snorted) and crack / freebase cocaine is generally smoked. Smoking freebase cocaine causes a strong, short-lived peak of about 3-5 minutes, while snorting cocaine provides a lower high with major effects lasting closer to 15 - 30 minutes.

Varies with dose and the tolerance of the user. Increases alertness, wakefulness, elevates the mood, mild to high degree of euphoria, increases athletic performance, decreases fatigue, clearer thinking, increases concentration, increases energy, increased irritability, insomnia, restlessness. With high doses may exhibit a pattern of psychosis with confused and disorganized behavior, irritability, fear, paranoia, hallucinations, may become extremely antisocial and aggressive.

Increases heart rate, blood pressure, body temperature, and sweating. Increases speed of respiration, dilates the pupils, decreased sleep and appetite. Can decrease seizure threshold and is associated with seizures, strokes, and heart attacks in susceptible individuals.

Although cocaine does not cause dangerous physical addiction, discontinuing regular use can lead to a wide varieties of (very) unpleasant withdrawal and craving symptoms, including: intense cravings for more cocaine, hunger, irritability, apathy, depression, paranoia, suicidal ideation, loss of sex drive, insomnia or excessive sleep, dizziness, shaking, and/or feeling cold. Although the withdrawal from heavy cocaine use is not as debilitating as the withdrawal from opiates or benzodiazepines, it is still usually quite unpleasant. Often, individuals simply take more cocaine to reduce these effects, leading to a pattern of habituation, dependence, and addiction.

As of 2015, a majority of powder cocaine outside of South America contains levamisole. Repeated use of levamisole can compromise the immune system.

Agitation, hostility, hallucinations, convulsions, high body tempertature (hyperthermia), stroke, heart attack, and possibly death.

People with latent congenital heart defects, high blood pressure, or thyroid problems are at higher risk of dangerous reactions and heart failure with the recreational use of cocaine.

Heavy, regular use of cocaine is known to cause restlessness, anxiety, hyperexcitability, paranoia, irritability, insomnia, weight loss, and a variety of other less acute psychological symptoms. Insufflation of any substance can lead to damaging the cartiledge and mucosa in the nose, eventually leading to a hole in the septum (the soft structure separating the nostils). If injected, cocaine use can lead to a wide variety of problems including life-threatening infections, shared needle-related blood diseases, etc.