After the Spanish conquest, Catholic missionaries campaigned against the cultural tradition of the Aztecs, dismissing the Aztecs as idolaters, and the use of hallucinogenic plants and mushrooms, like other pre-Christian traditions, was quickly suppressed.[7] The Spanish believed the mushroom allowed the Aztecs and others to communicate with devils. In converting people to Catholicism, the Spanish pushed for a switch from teonanácatl to the Catholic sacrament of the Eucharist. Despite this history, in some remote areas, the use of teonanácatl has persisted.[3]

The opium poppy was cultivated in lower Mesopotamia as long ago as 3400 BC.[79] The chemical analysis of opium in the 19th century revealed that most of its activity could be ascribed to the alkaloids codeine and morphine.

The onset of heroin's effects depends upon the route of administration. Studies have shown that the subjective pleasure of drug use (the reinforcing component of addiction) is proportional to the rate at which the blood level of the drug increases.[45] Smoking is the fastest route of drug administration, although intravenous injection results in a quicker rise in blood concentration.[46] These are followed by suppository (anal or vaginal insertion), insufflation (snorting), and ingestion (swallowing).

In the United States, approximately 1.6 percent of people have used heroin at some point, with 950,000 using it in the last year.[11][17] When people die from overdosing on a drug, the drug is usually an opioid and often heroin.[13][18]

It is reported that 15 of the 20 largest pharmaceutical companies have now used microdosing in drug development, and the use of the technique has been provisionally endorsed by both the European Medicines Agency and the Food and Drug Administration.