They're potent medications known as respiratory depressants: opiates. And if you take too much, they can stop some of your body's most basic functions.
"So breathing is just a reflex that the brain tells us when we're supposed to do that, and we don't consciously think about it," says Pima County Chief Medical Examiner, Dr. Gregory Hess.
And that's what makes these drugs so dangerous.
"People can just fall asleep and stop breathing and that's kind of the mechanism of death when they overdose on opiate medication," says Hess.
You've got oxycodone. You've got morphine. You've got hydrocodone. All big hitters in the world of opiates. But one of the most dangerous is fentanyl. So we wanted to know: what are the numbers like in Pima County?
In 2018 we had 45 deaths, overdose deaths, where we attributed fentanyl as a component of overdose," says Hess.
And that's the key phrase here: "Component of Overdose".
"Sometimes an overdose death is not from a single drug," says Hess. "It can be a poly drug or multi drugs involved in the death. So you look at those numbers and see that a death may involve meth and heroine, or meth and fentalyl."
And combinations like that may be more common than you might think.
"It's about 50/50. Single-drug versus poly-drug overdoses, in terms of whether or not more than one substance was present that may have contributed to the death," says Hess.
Regardless, fentanyl numbers are on the rise in Pima County. In the first quarter of 2019, there were 20 deaths. And medical experts say that's a lot!
"That's just a single quarter in 2019," says Hess. "So if there were 20 per quarter for the remainder of the year, we'd up to 80."
And another big problem with drugs like these is that often times people don't know what's actually in the drug they're buying.
"It's not like you're getting it from a U-S lab - from a company as a prescription from Walgreen's," says Hess. "So somebody will buy a pill or a powder and you don't know what's in it."
Not to mention, even a small amount of fentanyl can have the same effect as a larger amount of a different drug.
"So If someone is used to taking, or injecting, or smoking say a certain amount of heroin and they use the same amount of fentanyl, because fentanyl is so much more potent, they may die because of it," says Hess.
Looking forward, medical experts say without a crystal ball, it's hard to predict what's going to happen when it comes to opiates. But judging by the trends over the past few years, the number of fentanyl deaths in Pima County will only continue to rise.