Aspartame has been linked to cancer. Why is it in everything we drink?

It’s in cereal, sodas, and even your morning coffee. Here’s how an artificial sweetener called aspartame took over the world—in spite of long-standing health concerns.

Chemist Jim Schlatter had been putting in long hours at the lab. It was 1965, and the young scientist was attempting to synthesize a drug to treat ulcers. He’d been isolating various compounds along the way, and one of them had built up on the rim of a flask, getting on his bare fingertips as he worked.

At some point during his work—against lab regulations and common safety sense—Schlatter absentmindedly licked his finger to pick up a piece of paper more easily. It tasted sweet—much sweeter than sugar.

Schlatter had just discovered aspartame, an artificial sweetener that would be heralded as a breakthrough in food chemistry and weight loss. But the story of the compound isn’t all Diet Cokes and low-calorie coffees. Although the sweetener is the most popular on the market today—found in everything from ice cream to toothpaste—its future is being questioned after a recent report linking aspartame to cancer.

It wasn’t the first time that health concerns dogged aspartame.

Before aspartame, the most ubiquitous artificial sweetener was saccharin—also accidentally discovered in 1879 while German Russian chemist Constantin Fahlberg was working with coal tar. Saccharin rose to popularity worldwide during sugar shortages caused by the First World War, but by the 1960s the sweetener was being marketed to a new audience: women.

An obesity crisis was looming as the population had become more sedentary and mass marketing of food changed the way Americans ate. A parallel epidemic of fatphobia meant consumers were on the hunt for various weight loss aids—and increasingly turned to food made with artificial sweetener.

(How much of a role does genetics play in obesity?)

But not everyone loved calorie-free saccharin, which came with a bitter aftertaste, and the hunt was on for better substitutes. One contender, cyclamate, gained popularity in the diet soda industry. But the substance was banned in 1970 after claims it caused cancer in lab animals.

After Schlatter’s lab accident, he and his colleagues at pharmaceutical company G.D. Searle—then best known for developing the first commercially available birth control pill—began seeking U.S. Food and Drug Administration approval for the use of aspartame as a food additive. Aspartame held promise for as a good alternative to the popular, but now-banned cyclamate—a “super sweetener.”

“Will this restore to the nation’s figure-conscious sweet-tooths the low-calorie foods and drinks that were lost when cyclamate was banished from the supermarket?” asked one columnist in 1974. Aspartame’s supporters hoped the answer was yes.

After an extensive review process, the FDA in 1974 approved aspartame for use as a tabletop sweetener and for use in gum, breakfast cereals, and as an additive in certain foods like instant coffee and dairy products.

As Searle prepared to put aspartame on the market, the launch promised to be even sweeter when regulators threatened to pull saccharin based on similar concerns to those that had caused cyclamate’s downfall. As Searle stock skyrocketed, the buzz over aspartame grew. Congressional testimony on the dangers of a sugary diet also stoked public demand for the new sweetener.

But just months after aspartame was approved, the new sweetener’s safety was questioned by scientists who pointed to studies showing brain tumors, convulsions, and developmental disabilities in lab animals.

(Why low-calorie sweeteners might not be as good for us as we thought.)

The FDA first stayed, then revoked its approval, only reinstating it in 1981 after FDA commissioner Arthur Hayes, newly appointed by the business-friendly Reagan administration, overruled his agency’s experts. He approved aspartame for limited use in dry foods in 1981 and then for broader use as a beverage sweetener in 1983.

That’s when the floodgates opened. Searle marketed aspartame under the brand name Nutrasweet, and it began appearing on restaurant and dining room tables. And in 1983, Coca-Cola began using a saccharin-aspartame blend to sweeten its recently introduced sugar-free Diet Coke, which the company had developed with an eye to aspartame.

“We knew aspartame was going to happen; it was just a matter of when,” former Coca-Cola planning manager Jack Carew recalled. The company decided to launch its flagship diet drink before aspartame had been approved, in the hopes of incorporating it into the soda’s blend once it hit the market. It was a big bet on aspartame, which promised to be sweeter, better tasting, and cheaper than saccharin.

(Sugar doesn’t actually make kids hyper—here’s why so many believe it does.)

Diet Coke used aspartame as part of its marketing push, exhorting consumers to enjoy the beverage “just for the taste of it”—and its enormous popularity helped further fuel the aspartame market. Eventually, Diet Coke dropped saccharin entirely in favor of aspartame, though the fountain version does contain some saccharin for shelf stability and the company blends cyclamates into its formulation in countries that allow its use.

But the sweetener is yet again the topic of more modern controversy. Recently, the World Health Organization classified aspartame as “possibly carcinogenic to humans” even though officials said its safety “is not a major concern at the doses that are commonly used.” The FDA has objected to the WHO classification, saying that its officials “do not have safety concerns when aspartame is used under the approved conditions.”

Meanwhile, the drink that made the sweetener a household name could be endangered for other reasons. The Baby Boomers who made Diet Coke a hit are aging out of the product, Axios reports. Still, for now, aspartame remains a $9-billion-a-year business—proof of the world’s insatiable sweet tooth.