On September 1, the Food and Drug Administration issued warning letters to five sellers of powdered caffeine, warning them that their products are "dangerous and present a significant or unreasonable risk of illness or injury to consumers."

The letters criticize the ways the companies suggest customers measure a safe dose of caffeine powder, as it's impossible to accurately measure a safe dose using normal household tools.

Further, the FDA notes that companies sell potentially 125,000 "safe doses" of caffeine in one package, requiring "the consumer to use a precise scale to separate out a safe serving from [a] potentially lethal amount." The letters say that these count as violations and could result in the FDA seizing the products.

One company, Bridge City Bulk, told BuzzFeed News that they've stopped selling powdered caffeine in response to the FDA's letter.

The FDA has been concerned about easy access to deadly amount of caffeine since 2014, when two young men fatally overdosed on pure caffeine they'd bought online.

The powdered caffeine difference

Caffeine is the most commonly consumed psychoactive drug in the world, normally ingested while consuming chocolate, soda, and of course, coffee and tea.

In those forms, caffeine is mostly harmless.

It can keep you awake when you need to sleep and it can worsen anxiety, but it's hard to drink enough coffee to really hurt yourself — fatalities have occurred with the amount of caffeine in about 25 cups of coffee. Some other estimates say it would take the caffeine in 70-120 cups to kill an average person (the amount of caffeine in coffee varies significantly, with normal estimates ranging between 50 and 200 mg).

But in its pure form, caffeine can be deadly, and it's easy to underestimate its power. One teaspoon of pure caffeine contains 5,000 milligrams — the equivalent of 25-50 coffees. Between a teaspoon and a tablespoon could be enough to trigger an overdose or even a heart attack.

In 2014, the FDA called for that easy access to powdered caffeine to stop. In the agency's latest warning, they told the five companies they have 15 days to respond with the steps they've taken to ensure an end to the noted violations.

For now, pure powdered caffeine is still incredibly easy to get. In February, we found out exactly how easy it is when we purchased half a kilo on the internet.

Should this be legal?

We chose one of the online vendors selling bulk caffeine — in the time since since we made the purchase, some vendors have stopped selling powder, while others are only selling pre-dosed pills, safer since the customer doesn't have to measure the powder. You can't find powdered caffeine on Amazon (though they do sell caffeine pills and No-Doz, which are made of the same thing), but the vendor we chose has a good reputation on the nootropics subreddit for selling the actual chemical purchased.

A few days after placing the order, a package arrived, containing one 500g bag of synthetic caffeine and 50g of natural caffeine — all for $29.50, including shipping.

That 500g bag contains as much caffeine as is in 2,500 to 5,000 cups of coffee — or the same as 15,625 cans of Coca-Cola (or 11,904 Diet Cokes).

In the FDA's original safety warning about pure caffeine they noted that even in very small amounts it "may cause accidental overdose." Overdose symptoms include vomiting, diarrhea, stupor, disorientation, rapid or dangerously erratic heartbeat, seizures and death.

Michael Taylor, deputy commissioner for foods and veterinary medicine, told NPR that the FDA started asked companies to take pure caffeine off the market and that they have "started building a case to force companies to stop selling powdered caffeine" if those vendors aren't willing to voluntarily stop.

The latest warnings seem to be the steps they're taking to stop the companies that are still selling the powder.

A lethal dose

Here's the thing: Recommended doses range between 1/64 and 1/16 of a teaspoon. It's really hard to safely use that amount of caffeine powder, something that most of the companies acknowledge with warning labels (some small, some large). But almost no one has measuring utensils that small, and even if so, it's hard to say that they're accurate without weighing the powder (due to how densely they're filled).

Even with a kitchen scale we couldn't measure a safe dose, since its smallest unit of measure was grams and we'd need milligrams.

Without a milligram scale — not a common tool — there's actually no way to accurately measure a safe dose.

Even if you were trying to be careful, it'd be easy to take too much. I'm accustomed to quite a lot of caffeine, yet just tasting a tiny amount of the powder left me feeling like I'd had about four coffees. (Part of those effects could have been psychosomatic.)

In a certain sense, the appeal is clear — it's a cheap way to get caffeine into your system, and it's not accompanied by any of the sugar or other unhealthy ingredients in soda. But should it be sold in a formulation where the consumer has to measure the difference between a lethal and non-lethal dose?

The FDA doesn't think so, and many other people think it's dangerous and unreasonable for it to be legal.

Yet at the same time, there's an argument that Daniel Fabricant, executive director of the Natural Products Association (an industry group), expressed to NPR. "It is the dosage that makes anything a poison," he said, paraphrasing a common saying among toxicologists. "Take water... [or] salt for example — if you use too much, it creates problems. I think that's really the issue here. People safely use caffeine every day."

Of course, it's much easier to take a fatal dose of pure caffeine than any of those other things. But there are other substances that we can purchase legally that are toxic, like liquid nicotine or various cleaning products. Still, this might be the most toxic thing we have access to (per dose) that's meant for human consumption. (Rat poison, for example, is also highly toxic, but no one is blending a scoop into a post-workout smoothie.)

There isn't much regulation of supplements in general. Frequently, the FDA has no idea whether a supplement actually contains what people say it does, so cracking down on the sale of pure caffeine — as they seem to be doing — would be a big change.

It's not far-fetched to argue that our society wouldn't exist without caffeine. Indeed, Harvard neuroscientist Charles Czeisler thinks that along with the electric light, caffeine helped usher in the modern industrial era, and that we wouldn't have adapted to these clock-set work cycles that "allow" us to work all hours without it.

So it's powerful enough to change the world. Perhaps that caution about buying it in pure form by the bagful is warranted.

This post was updated on 9/1 to include the fact that Bridge City Bulk stopped selling powdered caffeine in response to the FDA's letter.