Just saw Goodfellas again, and in the end one of the detectives confirms (sarcastically) after a tiny dip into the powder and a lick of that finger that the captured powder is heroin. I’ve also seen that move in other Hollywood shows, sometimes by bad guys testing the purity of the stuff.
I’ve read, I think (God knows where) that cops weren’t allowed to do that because the powder could be cut with rat poison or other weird crap I never heard of.
What’s the Dope?
Leo
I’m not sure if it ever was, but it’s not done now - illegal drugs that can’t be easily identified by sight and smell are tested in the field by reagent tests and the like, and in the lab by gas chromatography/mass spectrometry (GC/MS). No need to taste anything.
From what cops have told me, it’s one of the biggest errors Hollywood tends to make in regards to their profession. For one thing, as you mentioned, the stuff could contain rat poison or some other type of caustic agent. For another thing ingesting the stuff could screw up any drug tests the officer might have to take.
If an undercover cop has no other choice that to sample an illegal narcotic to maintain his cover than he can do so, but needs to report it to his superiors as soon as possible so that it can be documented. That’s the only scenario I know of where a cop can “legitimately” sample drugs.
I doubt it ever happened in real life but I’ve heard that the cops aren’t really tasting for heroin. Because realistically, I don’t think heroin has a distinctive taste - most likely you’d only be tasting the filler used to cut it. What they’re supposedly doing is more like feeling it - they putting a little on their tongue and if their tongue goes numb that indicates the presence of heroin.
Cocaine would numb the tongue, as it functions as a local anesthetic, which was its original use. Heroin is an analgesic, however, and would not have a similar numbing property.
Been watching Training Day, have we? 
Police Officer Overdoses After Powder Goes Airborne During Heroin Bust
Daily Caller 05/15/2017
From above cite:
“They gave him one dose of Narcan here and then transported him to East Liverpool City Hospital, where they gave him three additional doses of Narcan,” East Liverpool Capt. Patrick Wright told WSB-TV. “We changed our procedures to [sic-Leo] where we used to field test-drugs. We don’t do that any longer because of accidental exposures.”
IIRC from the news, one of the concerns about fentynal (?) and derivatives is that a fatal dose is a tiny few crystals. Plus, one issue is that the stuff does not grind well so the quantity and distribution of active ingredients within a cut dose could be “variable”, which is what helps lead to so many overdoses on the street. You don’t really want to be finger-lickin’ good when a dip could give you close to a fatal dose, even ignoring issues with the added ingredients.
If an officer does ingest any drugs while working undercover, he’s taken off duty and put in the hospital, on worker’s compensation.
Fentanyl is absorbed through skin and mucous membranes; IDK if carfentanil is, but I do know it doesn’t take much to do awful things to people, and that’s why it’s used only for large-animal tranquilization.
Why would a dealer cut coke/heroin with rat poison? The idea is to keep your customers, not kill them.
Just think, I remembered I had an OP from seven years ago. Weird.
But “I” got over 11,000 happy customers!
This was the subject of a Straight Dope article.
The answer was that it’s extremely rare to find drugs laced with such poisons. As you suggest, dealers don’t want to kill their customers. Cecil guessed that on those rare occasions that it was done, the dealer was just looking to bulk up their supply with anything cheap that looked close enough to the real thing that it would pass an examination.
Frankly, I personally think it’s not that odd. If a dealer really wanted a healthy customer base they’d be selling vitamins and fresh vegetables, not coke and heroine. Dead customers are already a part of your business. And you might get away with blaming deaths on the customers overdosing.
Hi Leopold,I’m certain if I were in law enforcement I’d have to do that every time, just because.
In the column cited above:
I have read of heroin dealers cutting the product with Mannitol, a baby laxative. Maybe they figure it’s safer to inject than that stuff, or maybe it’s just to counter-act the constipation heroin causes.
There is a huge excluded middle between “healthy” and “dead”. It makes no sense to kill off your customer base. Unless it’s a desperate dealer who is only concerned with short term gains.
Nitpick: Henry Hill ( the main character in Goodfellas) was dealing cocaine, not heroin.
After hitting a sloppily rolled joint, I’ve had to remove bits of drug from my tongue.
I’d make a lousy cop.