Fentanyl: What is it, what are its effects, how is it consumed and how does it cause an overdose?

“Fentanyl is an opioid, a drug whose chemical structure is similar to morphine.” That’s how Valentín Islas, a chemist at the National Autonomous University of Mexico (UNAM), described the drug at the center of the overdose epidemic in the United States, of disputes between China and Mexico over the origin of its production, and of a trilateral strategy aimed at curbing trafficking into the U.S.

Fentanyl is a synthetic drug developed in the 1960s as a more potent and safer alternative to morphine, widely used during major surgical procedures and as an analgesic to treat severe pain, such as deep injuries, trauma and for palliative care.

Effects of fentanyl

Fentanyl’s journey in the human body begins immediately once it is consumed. While its pharmaceutical version is usually administered through injections, tablets, pills or transdermal patches prescribed by physicians with special permits, illegal fentanyl is marketed in powder, lozenges, in liquid form inside droppers or in drops applied on paper.

Like all opioids, fentanyl travels through the bloodstream and reaches the central nervous system in search of its target: opioid receptors. It binds to these elements of neurons, slowing their activity and decreasing the signals that transmit pain. “By interacting with the opioid receptor, [fentanyl] modulates pain. Among other things, it produces disengagement, sedation, lethargy and a sense of well-being,” Islas tells EL PAÍS. According to the U.S. National Institute on Drug Abuse (NIDA), other effects include euphoria, extreme happiness and confusion. However, the same potency that gives fentanyl an advantage over other opioids for medical use makes it potentially lethal in the illegal market.

Difference between pharmaceutical and illegal fentanyl

Fentanyl is the main driver of the opioid crisis in the United States, an unprecedented public health problem that in 2021 caused more than 107,000 overdose deaths, according to figures from the Centers for Disease Control and Prevention (CDC). Islas, a forensic chemistry expert, says there is a clear difference between pharmaceutical fentanyl and the illegal drug. While fentanyl for medical use is administered in controlled doses with a high margin of safety, the fentanyl on the streets is manufactured in clandestine laboratories, sometimes in a makeshift way.

“The therapeutic dose of fentanyl to produce the desired analgesic effect is 100 micrograms, and to produce respiratory depression almost eight times that amount is required,” he explains. “Pharmaceutical fentanyl maintains a very wide safety margin and has passed accredited and certified quality controls.” Not so the fentanyl sold on the illegal market, of which both the dosage and the substances used during its manufacture are unknown. What’s more, since fentanyl has become more widely used, the consumption of other opioids has become riskier: fentanyl is added to heroin and cocaine in a bid to enhance the effects of these drugs and maximize sales. This can be the decisive factor that leads to a life-threatening overdose.

How does fentanyl cause overdoses

The sense of well-being and euphoria produced by fentanyl can change dramatically after consuming an amount close to two milligrams, a lethal dose for most people. Represented in prevention campaigns as a dozen grains of salt or the amount of powder that fits on the tip of a pencil, this is a threshold that is easily crossed in the illegal market, where fentanyl in the form of pills, powder or combined with other drugs comes in heterogeneous doses: its concentration is impossible to calculate with the naked eye.

While therapeutic doses of pharmaceutical fentanyl modulate pain response and decrease nerve cell activity, toxic doses disrupt key motor functions in the body, especially those involved in breathing. “These neurons located at the level of the brain are the ones that control respiratory movements. If fentanyl occupies all the sectors of these neurons, they decrease their activity and all the motor functions they control are depressed,” Islas explains. “This means that respiratory movements are diminished.” Hence, far from the typical depictions in series and movies, the main symptoms of an overdose are related to weak breathing, a state similar to drowsiness. If a lethal dose of fentanyl runs its course without medical intervention, “it produces respiratory depression, then cardiac arrest follows, and finally, death.”

Symptoms of a fentanyl overdose

According to the CDC, the most common symptoms of a fentanyl overdose are constricted pupils and slow or weak breathing. Choking or gurgling sounds may also occur as signs of reduced respiratory function. In addition, a person suffering an overdose may fall asleep or lose consciousness. Their skin often feels cold, clammy and looks discolored, especially the lips and fingernails. If this occurs, CDC recommends calling 911, administering naloxone and trying to keep the person suffering an overdose on their side and awake. “It’s always best to use it [naloxone] if you think someone is overdosing,” the CDC states, pointing out that it has zero side effects.

Naloxone: how the antidote to fentanyl overdose works

Despite its potency, fentanyl poisoning does not always mean death. Naloxone, a drug capable of curbing the effects of opioids in the body in a matter of minutes, has become a lifesaver in the face of the unprecedented overdose epidemic in the United States. “Naloxone is an antagonist, a substance that reverses the effects of fentanyl. It is applied intravenously or with an intranasal spray and quickly reaches the blood and neurons located in the brain and displaces fentanyl from the opioid receptors, causing them to recover normal activity,” Islas explains.

At the end of March 2023, the U.S. Food and Drug Administration (FDA) approved naloxone for over-the-counter sale in an attempt to reduce fentanyl overdose deaths. Since then, pharmacies and convenience stores have marketed Narcan, a nasal spray manufactured by Emergent BioSolutions Laboratory. According to CDC guidelines, naloxone can restore a person to normal breathing within three minutes if administered in time.

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