Arecoline is a cholinergic agent, stimulant, and naturally occurring alkaloid found in areca (betel) nuts of the areca palm (Areca catechu) found in South and Southeast Asia. Its effects, depending on the dose, include stimulation, alertness, increased concentration, cognitive enhancement, elation, euphoria, pro-sexual effects, relaxation, reduced anxiety, and sedation, as well as addiction and withdrawal symptoms upon discontinuation. Its effects are described as subtle and it has been likened to a strong cup of coffee. There are also other active constituents of areca nuts, but arecoline is the key active component, with a percentage of ~0.3 to 0.6%. Areca nuts are administered by chewing for 5 to 20 minutes without swallowing.

Side effects of arecoline include hypersalivation, hypotension, vertigo, miosis, tremor, and bradycardia, among others. Other adverse effects can include extrapyramidal syndrome and seizures. Addiction and dependence can occur, with withdrawal symptoms including mood swings, anxiety, irritability, and insomnia. Rarely, psychosis can occur during withdrawal in heavy users. Areca nut use, the primary method of consuming arecoline, is highly associated with oral disease and oral cancer. Overdose of arecoline can be treated with antimuscarinic drugs like atropine or scopolamine.

The drug acts as a non-selective partial agonist of muscarinic and nicotinic acetylcholine receptors. The major metabolite of arecoline, arecaidine, is a GABA reuptake inhibitor. The subjective effects of arecoline appear to be mediated by muscarinic acetylcholine receptors and not by nicotinic acetylcholine receptors based on animal studies. However, its mechanism of action is still yet to be fully understood and other activities have also been described. The stimulant and addictive effects of arecoline are thought to be due to increased dopaminergic neurotransmission in the mesolimbic pathway of the brain. In terms of chemical structure, arecoline is closely related to nicotinic acid.

The use of arecoline, in the form of areca nuts, dates back several thousand years, including in Thailand, China, and Polynesia. Arecoline was first isolated in 1888 by Ernst Jahns and its synthesis was first proposed in 1891, with its chemical structure confirmed in 1907. The first complete synthesis was reported by Fritz Chemnitius at Jena University (Germany) in 1926. Arecoline, in the form of areca nuts, is used by more than 600 million people worldwide (~10–20% of the global population), and is the fourth most commonly used psychoactive drug in the world after alcohol, nicotine, and caffeine. Despite globalization, arecoline is unusual among recreational drugs in that its use is still predominantly confined to Asia, though its use has been increasing and spreading in part due to the Internet. Chewing areca nuts is said to be as familiar to various Asian peoples as chewing gum is to Americans. The countries in which areca nut production are highest include India, China, Myanmar, Malaysia, Indonesia, and Bangladesh. Arecoline and areca nut sale and consumption are not generally controlled throughout the world, with a few exceptions.

In many Asian cultures, the areca nut is chewed along with betel leaf to obtain a stimulating effect.

Arecoline has been used medicinally as an antihelmintic (a drug against parasitic worms). It paralyzes tapeworms.

Arecoline has been used in traditional medicine in Asia for thousands of years.

The LD₅₀ of arecoline is 100 mg/kg, when administered subcutaneously in mice. The minimum lethal dose (MLD) values of arecoline in mice, dogs, and horses is 100 mg/kg, 5 mg/kg and 1.4 mg/kg respectively.