Fentanyl is an opioid, a pain medication with a rapid onset that generally last less than an hour or two.

Fentanyl is available in a number of forms including by injection, skin patch, or can be absorbed through the tissues inside the mouth.

The side effects of fentanyl include nausea, constipation, sleepiness, and confusion.

More serious side effects include respiratory depression, serotonin syndrome, low blood pressure, and addiction.

Fentanyl works by activating μ-opioid receptors and is 75 times stronger than morphine.

Some fentanyl analogues may be as much as 10,000 times stronger than morphine.

Fentanyl was first made by Paul Janssen in 1960 and approved for medical use in the United States in 1968.

Its structure is similar to pethidine (meperidine), which acounts for its opioid activity.

In 2015, 1,600 kilograms (3,500 lb) were used globally.

As 2017 drew to a close, fentanyl was the most widely used synthetic opioid.

Fentanyl patches are on the World Health Organization's List of Essential Medicines, the most effective and safe medicines needed in a health system.

Unfortunately, Fentanyl is also made illegally and used as a recreational drug often mixed with heroin or cocaine.

In 2016 more than 20,000 deaths occurred in the United States due to overdoses of fentanyl and its analogues