Cocaine is a central nervous system stimulant and tropane alkaloid derived primarily from the leaves of two coca species native to South America: Erythroxylum coca and E. novogranatense. Coca leaves are processed into cocaine paste, a crude mix of coca alkaloids from which cocaine base is isolated and converted to cocaine hydrochloride, commonly known as "cocaine". Cocaine was once a standard topical medication as a local anesthetic with intrinsic vasoconstrictor activity, but its high abuse potential, adverse effects, and cost have limited its use and led to its replacement by other medicines. "Cocaine and its combinations" are formally excluded from the WHO Model List of Essential Medicines.

Street cocaine is commonly snorted, injected, or smoked as crack cocaine, with effects lasting up to 90 minutes depending on the route. Cocaine acts pharmacologically as a serotonin–norepinephrine–dopamine reuptake inhibitor (SNDRI), producing reinforcing effects such as euphoria, increased alertness, concentration, libido, and reduced fatigue and appetite.

Cocaine has numerous adverse effects. Acute use can cause vasoconstriction, tachycardia, hypertension, hyperthermia, seizures, while overdose may lead to stroke, heart attack, or sudden cardiac death. Cocaine also produces a spectrum of psychiatric symptoms including agitation, paranoia, anxiety, irritability, stimulant psychosis, hallucinations, delusions, violence, as well as suicidal and homicidal thinking. Prenatal exposure poses risks to fetal development. Chronic use may result in cocaine dependence, withdrawal symptoms, neurotoxicity, and nasal damage, including cocaine-induced midline destructive lesions. No approved medication exists for cocaine dependence, so psychosocial treatment is primary. Cocaine is frequently laced with levamisole to increase bulk. This is linked to vasculitis (CLIV) and autoimmune conditions (CLAAS).

Coca cultivation and its subsequent processes occur primarily Latin America, especially in the Andes of Bolivia, Peru, and Colombia, though cultivation is expanding into Central America, including Honduras, Guatemala, and Belize. Violence linked to the cocaine trade continues to affect Latin America and the Caribbean and is expanding into Western Europe, Asia, and Africa as transnational organized crime groups compete globally. Cocaine remains the world's fastest-growing illicit drug market. Coca chewing dates back at least 8,000 years in South America. Large-scale cultivation occurred in Taiwan and Java prior to World War II. Decades later, the cocaine boom marked a sharp rise in illegal cocaine production and trade, beginning in the late 1970s and peaking in the 1980s. Cocaine is regulated under international drug control conventions, though national laws vary: several countries have decriminalized small quantities.

Coca leaves have been used by Andean civilizations since ancient times. In ancient Wari culture, Inca culture, and through modern successor indigenous cultures of the Andes Mountains, coca leaves are chewed, taken orally in the form of a tea, or alternatively, prepared in a sachet wrapped around alkaline burnt ashes, and held in the mouth against the inner cheek; it has traditionally been used as an anorectic and to combat the effects of cold and altitude sickness, although its actual effectiveness has never been systematically studied.

Globally, in 2019, cocaine was used by an estimated 20 million people (0.4% of adults aged 15 to 64 years). The highest prevalence of cocaine use was in Australia and New Zealand (2.1%), followed by North America (2.1%), Western and Central Europe (1.4%), and South and Central America (1.0%). Since 1961, the Single Convention on Narcotic Drugs has required countries to make recreational use of cocaine a crime. In the United States, cocaine is regulated as a Schedule II drug under the Controlled Substances Act, meaning that it has a high potential for abuse but has an accepted medical use. While rarely used medically today, its accepted uses include serving as a topical local anesthetic for the upper respiratory tract and as an antihemorrhagic agent to stop bleeding in the mouth, throat, and nasal cavities.

It is legal for people to use coca leaves in the Andean Community, such as Peru and Bolivia, where they are chewed, consumed in the form of tea, or are sometimes incorporated into food products. Coca leaves are typically mixed with an alkaline substance (such as slaked lime) and chewed into a wad that is retained in the buccal pouch (mouth between gum and cheek, much the same as chewing tobacco is chewed) and sucked of its juices. The juices are absorbed slowly by the mucous membrane of the inner cheek and by the gastrointestinal tract when swallowed.

Coca herbal infusion (also referred to as coca tea) is used in coca-leaf producing countries much as any herbal medicinal infusion would elsewhere in the world. The free and legal commercialization of dried coca leaves under the form of filtration bags to be used as "coca tea" has been actively promoted by the governments of Peru and Bolivia for many years as a drink having medicinal powers. In Peru, the National Coca Company, a state-run corporation, sells cocaine-infused teas and other medicinal products and also exports leaves to the U.S. for medicinal use. The effects of drinking coca tea are mild stimulation and mood lift.