Aspartame and Cancer: What IARC's Review Means

This page is for anyone who saw the 2023 headlines about aspartame and cancer. It explains what the two WHO reviews found, where the FDA stands, and who must avoid aspartame.

On July 14, 2023, two bodies published findings on aspartame at once. That timing is why the news coverage got confusing.

IARC is the World Health Organization's cancer research agency. It classified aspartame as possibly carcinogenic to humans, Group 2B.

JECFA is the Joint FAO/WHO Expert Committee on Food Additives. It kept the acceptable daily intake at 40 mg per kilogram of body weight.

The two bodies ran independent but complementary reviews. They answered two different questions. That difference is the whole story here.

Aspartame is an artificial sweetener, in use since the 1980s. It is a dipeptide. That means it is built from two amino acids: phenylalanine and aspartic acid. Both turn up naturally in protein foods.

It is about 200 times sweeter than table sugar, so very little is needed. It is also not heat stable. It loses its sweetness when heated. That is why it is rarely used in baked goods.

WHO's list of products holding it is longer than most people expect. It covers:

• diet drinks
• chewing gum
• gelatin
• ice cream, yogurt, and other dairy
• breakfast cereal
• toothpaste
• medicines such as cough drops and chewable vitamins

IARC's label rested on three separate findings of limited evidence:

• Limited evidence in humans. The cancer was hepatocellular carcinoma, a type of liver cancer.
• Limited evidence in lab animals.
• Limited evidence on how cancer might be caused.

That was IARC's first-ever review of aspartame. Mary Schubauer-Berigan of the IARC Monographs program framed it as a call for research. Limited evidence in all three areas, she said, shows how much more work is needed.

Two points about Group 2B are worth keeping. It is the third of four levels, not the top. And it is used in one of two cases. Either human evidence is limited but not convincing, or animal evidence is convincing. Not both.

IARC is also blunt about what its labels do not do. They show how strong the evidence is that something can cause cancer. They say nothing about the risk at any real exposure level. Our explainer on hazard versus risk unpacks that split.

JECFA asked a different question. How likely is harm at the amounts people really consume?

Its answer was short. The data gave no reason to change the existing acceptable daily intake of 0 to 40 mg per kilogram of body weight. This was JECFA's third review of aspartame. Moez Sanaa of WHO summed up the reading. The evidence of a link between aspartame and cancer in humans is not convincing.

Francesco Branca directs WHO's Department of Nutrition and Food Safety. He put both findings in one line. Safety is not a major concern at the doses commonly used. But possible effects have been described, and they need more and better studies.

This is the part that turns a label into something usable.

Start with JECFA's own example. A can of diet soft drink holds 200 or 300 mg of aspartame. Take an adult weighing 70 kg, about 154 pounds. That person would have to drink more than 9 to 14 cans in a day to pass the 40 mg limit. That assumes no aspartame from any other food.

The FDA runs its arithmetic on packets instead. Its limit is 50 mg per kilogram. A 60 kg person, about 132 pounds, would need 75 tabletop sweetener packets in one day to reach it.

The FDA's limits for some other sweeteners are lower. Acesulfame potassium and saccharin sit at 15 mg per kilogram. Sucralose sits at 5. Neotame sits at 0.3.

The FDA's limit is 50 mg per kilogram per day, not 40. Both numbers are real. They come from different reviews.

The FDA has regulated aspartame as a food additive since 1974. The first approval covered tabletop use, chewing gum, cold cereals, and dry mixes for products such as drinks, gelatins, and puddings. It became a general-purpose sweetener in 1996. The agency says it has reviewed more than 100 studies. Those covered cancer, metabolism, and effects on the reproductive and nervous systems.

The FDA also disagreed in public with IARC's basis. It says it reviewed the material in IARC's 2021 review when it first appeared. It then identified significant shortcomings in the studies IARC relied on. The FDA states it has no safety concerns when aspartame is used under approved conditions.

This has nothing to do with cancer. People with phenylketonuria, or PKU, must avoid aspartame. PKU is a rare inherited disorder. It makes phenylalanine hard to process, and untreated, it can build up to harmful levels in the body (MedlinePlus).

Two practical facts follow. US labels must state that a product contains phenylalanine. And newborns are screened for PKU with a heel-prick blood test before they leave the hospital.

The researchers named the gaps themselves. That is more useful than a verdict. JECFA asked for better studies with longer follow-up. It asked for repeated diet questionnaires in cohorts that already exist. It also asked for randomized trials. Those should include the pathways tied to insulin control, metabolic syndrome, and diabetes.

Aspartame carries a Group 2B label. That label rests on limited evidence in three separate areas. The cancer behind it is liver cancer. JECFA and the FDA both kept their intake limits. JECFA's example is that a 70 kg adult would need more than 9 to 14 cans of diet soda in a day to pass the 40 mg per kilogram limit, assuming no other aspartame in the diet. For a sweetener with a similar history, see our page on saccharin.

• World Health Organization, IARC, and FAO/WHO JECFA, Aspartame hazard and risk assessment results released, July 14, 2023, accessed August 6, 2026
• U.S. Food and Drug Administration, Aspartame and Other Sweeteners in Food, accessed August 6, 2026