The Harrison Narcotics Tax Act (Ch. 1, 38 Stat. 785) was a United States federal law that regulated and taxed the production, importation, and distribution of opiates and coca products. The act was proposed by Representative Francis Burton Harrison of New York and was signed into law by President Woodrow Wilson on December 17, 1914.

"An Act To provide for the registration of, with collectors of internal revenue, and to impose a special tax on all persons who produce, import, manufacture, compound, deal in, dispense, sell, distribute, or give away opium or coca leaves, their salts, derivatives, or preparations, and for other purposes." In Webb v. United States, the act was interpreted to prohibit prescribing maintenance doses for narcotics unless it was intended to cure the patient's addiction.

The Harrison anti-narcotic legislation consisted of three U.S. House bills imposing restrictions on the availability and consumption of the psychoactive drug opium. House Resolution (H.R.) 1966 and H.R. 1967 passed conjointly with H.R. 6282 (the Opium and Coca Leaves Trade Restrictions Act).

Although technically illegal for purposes of distribution and use, the distribution, sale and use of cocaine was still legal for registered companies and individuals.

Following the Spanish–American War and the Philippine–American War, the Philippines saw a proliferation of opium use. A cholera outbreak in 1902 further strengthened this tendency due to the astringent properties of opium.

Charles Henry Brent was an American Episcopal bishop who served as Missionary Bishop of the Philippines beginning in 1901. He convened a Commission of Inquiry, known as the Brent Commission, for the purpose of examining alternatives to a licensing system for opium addicts. Although Governor William Taft supported this policy, Brent opposed it "on moral grounds". The Commission recommended that narcotics should be subject to international control. The recommendations of the Brent Commission were endorsed by the United States Department of State and in 1906 President Theodore Roosevelt called for an international conference, the International Opium Commission, which was held in Shanghai in February 1909. A second conference was held at The Hague in May 1911, and out of it came the first international drug control treaty, the First International Opium Convention of 1912.

Between 1895 and 1900 there were probably more people using morphine in the United States than today on a per capita basis. Opium usage peaked in 1896 and then began to decline gradually. Oliver Wendell Holmes Sr., then dean Harvard Medical school, blamed the prevalence of opiate addiction on ignorance. As awareness of the addictiveness of morphine and patent medicines grew public opinion in the 1890s was in favor of state laws restricting morphine. Demand gradually declined thereafter in response to mounting public concern, local and state regulations, and the Pure Food and Drug Act of 1906, which required labeling of patent medicines that contained opiates, cocaine, alcohol, cannabis and other intoxicants. By 1914, forty-six states had regulations on cocaine and twenty-nine states had laws against opium, morphine, and heroin.

In the 1800s opiates were mostly unregulated drugs. Morphine use had spread rapidly during and after the Civil war. The consumption of household remedies and marketed syrups containing morphine was commonplace and mostly associated with the upper and middle class of society. Many women (not all) who were prescribed and dispensed legal opiates by physicians and pharmacist for "female problems" (probably pain at menstruation) became addicted. It's likely many who became addicted initially did not know what the syrups and concoctions contained.