In July 2023 two arms of the World Health Organization published findings about aspartame on the same day, and the headlines picked one of them. IARC classified aspartame as possibly carcinogenic to humans. JECFA, the expert committee that assesses intake, left the acceptable daily intake exactly where it was. Both are real, both were deliberate, and understanding why they are not in conflict is the whole of this article.
Hazard is not risk
IARC assesses hazard: whether something is capable of causing cancer under some conditions. It does not assess how likely that is at the doses people actually encounter. That is why its categories group substances that feel wildly different in everyday terms — the classification reflects how strong the evidence is, not how dangerous the thing is.
Group 2B, where aspartame landed, is the category for limitedevidence. It is the weakest of the categories that indicate any concern at all. Reading it as “the WHO says aspartame causes cancer” inverts what the classification is for.
Riskis the other question: given a real diet, how much harm is plausible? That is JECFA's job, and its answer was to reaffirm an acceptable daily intake of 40 mg per kilogram of body weight per day. For a 70 kg adult that is 2,800 mg daily, sustained. The committee said it found no convincing reason to change the figure.
So is aspartame bad for you?
On the evidence as it stands: there is limited evidence that it could be a hazard, and no basis to say typical intakes are unsafe. That is an unsatisfying answer, and it is the accurate one. Anyone giving you a cleaner answer in either direction has decided something the assessment bodies did not.
What we would not tell you is that a diet drink is therefore good for you. Approval is a toxicological statement, not a nutritional one. A sweetened drink displaces water and trains a preference for sweetness; health authorities have separately published guidance advising against relying on non-sugar sweeteners as a weight-management strategy. That is a different argument from the cancer one and it should be made separately, because collapsing them is how the public conversation got this confused.
Where aspartame sits under NOVA
Here the answer is clean. Non-sugar sweeteners are among the clearest NOVAgroup 4 markers, because the definition turns on purpose. A sweetener exists to make a formulation taste of something it is not — the textbook cosmetic additive. A drink containing aspartame is ultra-processed.
Note how little that verdict tells you about safety. NOVA classifies processing, not toxicity, and the two questions have genuinely different answers here: ultra-processed by construction, not shown to be harmful at normal intakes. Keeping those apart is the difference between informing someone and frightening them. See our additives guide for the other classes, and fizzy drinks for the category as a whole.
What Cull shows you
Cull names aspartame when it finds it, flags it as a sweetener, and counts it towards the processing assessment — because under NOVA it genuinely is a marker. It does not attach a health warning to it, because the evidence does not support one at typical intakes. Where the science is unresolved, saying so is the honest option.