Fentanyl is a highly potent synthetic (lab-made) opioid. It has been used as an analgesic (pain-killing) medicine since the 1960s.
Recently fentanyl use has emerged in non-medicinal drug markets, either sold as fentanyl or more commonly found as an adulterant (unexpected ingredient) in other drugs. In many countries, fentanyl has been detected as products mis-sold as heroin, benzodiazepines (such as diazepam and etizolam), cocaine and gabapentinoids.
It is active in lower doses than heroin so a much smaller dose is needed to feel the effects. Anyone who takes drugs should be aware of the risks of adulterants, test the drugs, start with a test dose and use fentanyl test strips.