Let’s talk about fentanyl. It is a very powerful ligand for opioid receptors, and it has very powerful pharmacological activity. As the world knows, that activity includes a very real possibility for addiction, as with all pain-relieving opioid agonists, and it also comes with the other dangerous side effects such as respiratory depression. That’s how overdoses with such drugs typically kill people – they lose consciousness and stop breathing. This seems to be through loss of sensitivity to carbon dioxide levels – the “need a deep breath” reflex just does not kick in, and oxygen levels continue to drop. In opioid use for pain this effect tolerates out rather quickly, but a large dose can cause this effect even in people who have developed a high opioid tolerance in general. It’s thought that reduced sedation in such cases (another typical opioid side effect) makes that particular warning sign less effective. Another problem with overdoses is what’s called “wooden chest syndrome”, where the abdominal muscles became so rigid that breathing deeply becomes difficult or impossible. That one seems to only occur with the most potent synthetic ligands; it’s much less common with something like heroin.
For these reasons and others, opiods are dangerous substances to handle, and because of fentanyl’s potency it is even more dangerous than morphine or heroin (and those two are not exactly benign things to deal with). Fentanyl overdoses are also unpredictable because of side reactions with other drugs. Caution in being exposed to fentanyl is completely appropriate, and in light what I’ll be saying in the rest of the post, I want to make that part very clear. This is a dangerous drug and should be dealt with that way. But over the years an entire mythology has grown up around the drug because of these dangers, and this has had some rather odd consequences. Too many people now believe that they can be immediately killed by a fentanyl overdose from any sort of skin contact with the drug, and that’s just not true. It’s potent and toxic for sure, but you have to be dosed with it for that to happen.
This has come to more attention since the CDC recently removed a video from the NIOSH site that it says “mischaracterizes” the dangers of fentanyl exposure for police and first responders. There are many such videos of police officers quickly showing overt symptoms or even collapsing after exposure to minute quantities of fentanyl – or even just possible fentanyl – and these are just not pharmacologically possible. Fentanyl is not absorbed through the skin like this. Yes, there are indeed fentanyl skin patches for hospital pain relief, but these are formulated with other agents to make the skin more permeable under the patch (as are all such skin-patch dosage forms). Think about it: you do not see opioid addicts rubbing small bits of fentanyl on the backs of their hands for a quick hit. But this hysteria – which is what to call it – has spread to the point that random people are fainting when they think they’ve been exposed by (for example) picking up money off the floor.
For some perspective, I recommend this paper, which details an exposure to a 10mg/mL solution of fentanyl citrate all over a person’s hand. If any of these fentanyl-collapse videos had anything behind them, this patient should have hit the floor pronto. Instead, they washed off his hand, and he showed no signs of opioid exposure at all. The paper goes on to estimate that you would need an extended soaking in such a solution to reach any sort of dangerous blood levels, and it provides references to show that toxicologists have been trying to train first responders out of their fentanyl fears for several years now. Apparently to no effect. You know what has the lowest IC50 of all? Paranoia.
