Aspartame cancer risk and what IARC's Group 2B rating means
Aspartame cancer evidence led IARC to Group 2B, but intake limits remain unchanged. See what regulators say about diet drinks, safety and food labels.
No regulator has found that aspartame causes cancer at the amounts people actually consume. IARC's 2023 Group 2B rating, "possibly carcinogenic to humans", reflects limited evidence of a hazard, not the risk at real intakes. JECFA kept its intake limit unchanged, and the FDA says approved uses are safe.
What IARC decided in 2023
On 14 July 2023 the International Agency for Research on Cancer classified aspartame as Group 2B. The evidence was rated "limited" on all three lines IARC looks at, according to the joint WHO summary of findings:
- In humans, for hepatocellular carcinoma (a type of liver cancer). This rested on three studies that used artificially sweetened drinks as a stand-in for aspartame intake. Chance, bias or confounding could not be ruled out.
- In experimental animals, with concerns about study design and how tumours were diagnosed.
- On mechanisms, mainly oxidative stress.
The same summary says IARC's groups "do not indicate the degree of risk of developing cancer at a given exposure level". The full assessment appeared in IARC Monographs Volume 134 in 2024.
Is aspartame bad for you? What the risk assessors said
The FDA describes its acceptable daily intake (ADI) as the amount considered safe to consume each day over a lifetime. JECFA, the joint WHO and FAO expert committee, reviewed aspartame in 2023. It found "no convincing evidence from experimental animal or human data that aspartame has adverse effects after ingestion". It reaffirmed the ADI of 0 to 40 mg per kg of body weight per day (summary of findings). The full report is WHO Technical Report Series 1050.
With a can of diet soft drink containing 200 or 300 mg of aspartame, a 70 kg adult would need more than 9 to 14 cans a day to exceed that ADI, assuming no other intake (WHO release). WHO and IARC still asked for more and better studies.
On 10 December 2013, EFSA's re-evaluation of aspartame (E 951) concluded that the current ADI of 40 mg/kg of body weight per day is protective for the general population, and ruled out a risk of gene damage or cancer. In its 10 September 2026 announcement on the aspartame-acesulfame salt (E 962), EFSA reconfirmed the aspartame ADI after reviewing literature up to June 2025. It said the evidence "does not support a causal link" between current dietary exposure and cancer, and it recommended reviewing the arsenic and lead limits in the E 951 specifications (plain-language summary).
The FDA says it "disagrees with IARC's conclusion", pointing to "significant shortcomings in the studies on which IARC relied". Its scientists "do not have safety concerns when aspartame is used under the approved conditions of use". The FDA's ADI is 50 mg/kg bw/day. JECFA and EFSA use 40. Each figure is that body's own limit.
The UK Committee on Carcinogenicity, which advises the Food Standards Agency, concluded on 20 July 2023 that "no regulatory action was required". FSANZ said on 24 July 2023 that the limits in the Food Standards Code are "appropriate and current". Health Canada took no further action and keeps an ADI of 40. None of these regulators changed its rules after the IARC listing.
Does Diet Coke cause cancer?
The WHO assessment doesn't establish that aspartame-sweetened diet drinks cause cancer at usual intakes. Recipes vary by country, so check the ingredients list for aspartame. Read the 9 to 14 can figure as an ADI illustration, not as advice to drink up to 14 cans.
The FSA says only people diagnosed with phenylketonuria (PKU) need to avoid aspartame, because they cannot consume phenylalanine. EFSA's ADI does not apply to them. The phenylalanine warning is about PKU, not cancer.
Legal status and labels after the IARC listing
The IARC classification itself does not require reformulation or a new cancer warning. Existing authorisation conditions and labelling duties still apply.
In the EU, aspartame (E 951) is still listed in Annex II of Regulation (EC) No 1333/2008 (consolidated text of 18 August 2026) across 35 food categories. In flavoured drinks it is allowed up to 600 mg/l, and only in energy-reduced products or those with no added sugar. Table-top sweeteners containing it must say "contains a source of phenylalanine" under Article 23(3)(b). On other foods, labelling comes from Annex III of Regulation (EU) No 1169/2011:
- "with sweetener(s)", or "with sugar(s) and sweetener(s)" where both are present
- "contains aspartame (a source of phenylalanine)" where aspartame appears only as an E number
- "contains a source of phenylalanine" where it is listed by name
In the US, 21 CFR 172.804 allows aspartame as a sweetener and flavour enhancer under good manufacturing practice. Labels must read "PHENYLKETONURICS: CONTAINS PHENYLALANINE".
Other sweeteners: saccharin (Sweet'N Low), sucralose, stevia, acesulfame K
The evidence on artificial sugar and cancer differs by sweetener. The FDA lists the US ADIs and permitted uses below. EU limits come from the EFSA assessments linked after the table.
| Sweetener | IARC | EU ADI (mg/kg bw/day) | US status |
|---|---|---|---|
| Saccharin (E 954) | Group 3, not classifiable | 9 | ADI 15, warning label repealed 2000 |
| Sucralose (E 955) | Not classified | 15 | ADI 5, approved 1998 |
| Steviol glycosides (E 960a-d) | Not classified | 4 (as steviol) | High-purity extracts only |
| Acesulfame K (E 950) | Not classified | 15 | ADI 15, general-purpose approval 2003 |
Sweet'N Low is a saccharin brand. It sits in IARC Group 3 (Volume 73, 1999). The rat bladder tumours that caused the old scare arise by mechanisms not relevant to humans, and saccharin was dropped from the US Report on Carcinogens in 2000. The US warning label requirement was repealed by Public Law 106-554 on 21 December 2000. EFSA raised its ADI from 5 to 9 on 15 November 2024.
Sucralose was re-evaluated by EFSA on 17 February 2026. The ADI stays at 15 and current uses are safe. But EFSA could not confirm the safety of extending use to energy-reduced fine bakery wares, because chlorinated compounds may form on heating. The NCI says a range of studies have found no evidence that sucralose causes cancer in humans.
Stevia, authorised in the EU as steviol glycosides, has no IARC cancer classification. E 960b (from fermentation) was added by Regulation (EU) 2025/652. EFSA refused a 2024 request to raise the ADI. JECFA uses 0 to 4 mg/kg of body weight, expressed as steviol, which is also the EU figure. In the US, the FDA has not questioned GRAS notices for high-purity steviol glycosides, but stevia leaf and crude extracts are not GRAS and may not be imported for use as sweeteners.
Acesulfame K had its EU ADI raised from 9 to 15 in 2025. The NCI reports that in the French NutriNet-Santé cohort, adults who consumed acesulfame K had a slightly higher overall cancer risk than those who did not. No other studies have examined whether it is associated with cancer in people.
The WHO sweetener guideline is about weight
On 15 May 2023 WHO issued a conditional recommendation against using non-sugar sweeteners to control body weight or reduce the risk of noncommunicable diseases, except for people with pre-existing diabetes. WHO said the evidence might be confounded by who uses these sweeteners and how. It is not a cancer classification.
If you need to trace the aspartame rules for a specific market or food category, RegAffairs AI has a cited answer to this question that opens each source document.