Fentanyl is a powerful synthetic opioid created in 1960, originally introduced as an anesthetic. Because it is synthetic, it can be easily and inexpensively made in a lab. It was approved by the FDA in the early 1990’s for use as a painkiller and anesthetic. It works by binding to opioid receptors in the brain, but it does so faster — and in much smaller doses — than morphine or heroin. Like other opioids, it boosts levels of the chemical dopamine, which controls feelings of reward, pleasure, euphoria, and relaxation.

Today, Fentanyl is typically prescribed to treat patients who need long-term, around-the-clock relief from severe pain. When used for medical purposes, it is often given in a shot, a patch on the skin, or in lozenges.

China has become a global source of Fentanyl because (a) it can be easily and inexpensively made in a lab; and (b) the vast chemical and pharmaceutical industries in China are lightly regulated.

Some Fentanyl comes straight to the United States from China, while other shipments come in from China to Mexico (and to a lesser extent) Canada before making its way into the U.S.

There currently is no tariff on Fentanyl imported into the U.S. from any point of origin, which indicates that the Trump administration has missed a major revenue opportunity.