TL;DR
In July 2023, IARC reclassified aspartame (E951) as Group 2B — possibly carcinogenic to humans — based on limited evidence in humans for liver cancer. The same day, JECFA reviewed the same data and concluded the existing acceptable daily intake of 40 mg per kilogram of body weight per day did not need to change. UK and EU regulators have not changed their permitting position. We don’t tell you it is “safe” or “not”. We describe what each body said, the numbers behind the ADI, and where the evidence sits.
Two assessments, the same day, different questions
On 14 July 2023, two WHO-affiliated bodies published assessments of aspartame on the same day. The headlines led with the IARC classification; the JECFA conclusion landed beneath it. The two bodies were not contradicting each other. They were answering different questions on the same evidence.
- IARC (International Agency for Research on Cancer) does hazard identification: can this substance cause cancer in any circumstance, at any dose? They classify, they don’t set intake levels.
- JECFA (Joint FAO/WHO Expert Committee on Food Additives) does risk assessment: at what dose, under typical exposure, does this substance pose a meaningful risk? They set the acceptable daily intake.
Read together, the 2023 conclusions say: there is now limited evidence in humans that aspartame can cause cancer (specifically hepatocellular carcinoma); the existing ADI of 40 mg/kg body weight per day still appears appropriate based on the dose-response data reviewed.
What IARC Group 2B actually means
IARC has four categories. Group 1 is “carcinogenic to humans” — the evidence is sufficient (tobacco, processed meat, alcohol, asbestos). Group 2A is “probably carcinogenic” — sufficient animal evidence, limited human evidence (red meat, hot drinks above 65°C). Group 2B is “possibly carcinogenic” — limited human evidence, less than sufficient animal evidence. Group 3 is “not classifiable.”
Group 2B in context
Group 2B contains hundreds of agents. Alongside aspartame sit aloe vera whole leaf extract, traditional Asian-style fermented vegetables, lead, gasoline engine exhaust, and radio-frequency electromagnetic fields (the kind mobile phones emit). The classification is a statement about the strength of the published evidence, not a verdict about how risky a thing is at the doses people actually encounter. That dose question is JECFA’s job.
For aspartame specifically, the IARC working group cited three observational studies linking artificially sweetened beverages to hepatocellular carcinoma (a type of liver cancer). The studies could not rule out confounding — people who drink a lot of diet sodas may differ from non-consumers in other ways — which is why the evidence was rated “limited” rather than “sufficient.”
What JECFA said the same day
JECFA reviewed the same body of literature and the dose data and concluded that “the available evidence does not indicate a need to change the existing acceptable daily intake of 0–40 mg per kilogram of body weight per day.” Aspartame’s ADI is one of the most-studied of any food additive, dating back to the 1980s and revisited multiple times since. The 2023 review did not move it.
The ADI carries a 100-fold safety factor: it is set at one one-hundredth of the highest dose at which no adverse effect was observed in animal studies. The factor is standard practice in food-additive risk assessment and exists to absorb individual variation, lifetime exposure, and unknown unknowns.
What 40 mg per kilogram a day looks like in real cans and packs
For a 70 kg adult, the JECFA ADI works out to roughly 2,800 mg of aspartame per day, every day, across a lifetime. A typical 330 ml diet drink in the UK contains about 180–200 mg of aspartame depending on brand and formulation. So a 70 kg adult drinking nothing but diet sodas would need around 14 cans every day to reach the ADI from drinks alone.
| Product | Typical aspartame per serving | Servings to reach ADI (70 kg adult) |
|---|---|---|
| 330 ml diet cola (typical UK formulation) | ~180–200 mg | ~14 cans |
| 250 ml sugar-free squash (diluted as recommended) | ~50 mg | ~56 glasses |
| Tabletop sweetener tablet (Canderel, etc.) | ~18 mg | ~155 tablets |
| Sugar-free chewing gum (one piece) | ~6 mg | ~467 pieces |
| Low-calorie yoghurt (125 g pot) | ~50 mg | ~56 pots |
Per-product aspartame content varies by brand and recipe; the figures above are typical UK values. EFSA’s 2013 European exposure assessment found that even the highest aspartame consumers in Europe reached around 36% of the ADI at the extreme end. Most consumers are nowhere near it.
Where you find aspartame on UK shelves
Aspartame is widespread but always declared. UK labelling rules require it to appear in the ingredients list either by name (“aspartame”) or by its E number (E951), and any product containing it must also carry the labelling phrase “contains a source of phenylalanine.” The places it turns up most:
- Diet sodas and zero-sugar fizzy drinks — Diet Coke, Pepsi Max, Coke Zero (aspartame is usually blended with acesulfame K for taste).
- Sugar-free chewing gum — most major UK brands.
- Tabletop sweeteners — Canderel, NutraSweet, some Hermesetas products.
- Sugar-free squashes and cordials — Robinson’s, Vimto, supermarket own-brand.
- Low-calorie and “diet” yoghurts — especially fruit-flavoured pots.
- Some “diet” cereals and reduced-sugar breakfast products.
- Sugar-free sweets, mints and chewing gum — Polo Sugar Free, Tic Tac, Smint.
- Some sugar-free medicines — certain liquid medicines and chewable tablets formulated to be palatable without sugar.
Who should pay closer attention
Aspartame and PKU — the one clear-cut group
People with phenylketonuria (PKU) — an inherited metabolic condition affecting roughly 1 in 10,000 UK births — must avoid aspartame. Their bodies cannot properly metabolise phenylalanine, one of aspartame’s breakdown components, and accumulation is harmful. UK newborns are screened on the NHS heel-prick test at around 5 days old. If a child has PKU, the family will be under specialist metabolic team care and given strict dietary guidance. The “contains a source of phenylalanine” labelling phrase exists for exactly this group.
Pregnancy. The NHS does not restrict aspartame in pregnancy within the ADI. Some women choose to limit it on personal preference; that is a personal choice, not an NHS instruction. If you want individual guidance, speak to your midwife or GP.
Self-reported sensitivity. Some people report headaches or digestive discomfort after consuming aspartame. Double-blind trials have not consistently replicated those reports. If a particular food or drink reliably makes you feel unwell, it is reasonable to avoid it regardless of what the population data shows — but that is a personal call about your own response, not a medical claim about aspartame in general.
What the science doesn’t settle
IARC and JECFA looked at the same evidence and drew different conclusions because they were asking different questions. That isn’t a contradiction — but it is a real gap. The 2023 IARC reclassification is, in plain terms, a signal that the human evidence base has grown enough to warrant a closer look, and that more long-term human studies would be valuable.
Other open questions: cocktail effects with other sweeteners and additives are less well-studied than aspartame on its own; how aspartame interacts with the gut microbiome is an active research area with mixed findings; and the observational signal IARC cited for liver cancer is the kind of association that calls for prospective replication, not a settled finding.
UK and EU regulators — the FSA, EFSA, and FSANZ — have not changed their permitting position since the 2023 review. That is a description of where regulators stand, not a verdict from us.
How NutraSafe handles aspartame
If you scan a UK barcode in our app, every E-number in the ingredients line is surfaced and labelled with what it is and what it’s used for. Aspartame shows up wherever it’s declared, with the IARC and JECFA positions described in plain English. We don’t print “safe” or “unsafe” verdict pills. We give you the regulatory facts, the research signal, and the option to filter products containing aspartame out of your diary or scans if that’s the call you want to make for yourself.
If you’re tracking sweetener intake more broadly, we cover the full landscape in our guide to whether E numbers are bad for you and a side-by-side look at artificial sweetener side effects in the UK.
Frequently asked questions
What did IARC and JECFA actually say about aspartame in 2023?
On 14 July 2023, IARC classified aspartame as Group 2B — possibly carcinogenic to humans — based on limited human evidence for hepatocellular carcinoma. The same day, JECFA reviewed the same data and concluded the existing ADI of 40 mg/kg body weight per day did not need to change. They were answering different questions: IARC asked whether aspartame can cause cancer in any circumstance; JECFA asked whether typical exposure poses a risk.
What does Group 2B mean?
Group 2B is IARC’s category for substances with limited evidence of carcinogenicity in humans and less than sufficient evidence in animals. It is not Group 1 (e.g. tobacco, processed meat, alcohol) and not Group 2A (e.g. red meat, hot drinks above 65°C). Other Group 2B entries include aloe vera whole leaf extract, traditional Asian-style fermented vegetables, and radio-frequency electromagnetic fields. The classification flags the evidence base, not a verdict on everyday risk.
How many diet sodas would a 70 kg adult need to drink to hit the JECFA ADI?
The ADI of 40 mg per kilogram per day works out to about 2,800 mg for a 70 kg adult. A 330 ml UK diet cola contains roughly 180–200 mg of aspartame, so reaching the ADI from drinks alone would mean around 14 cans every day. EFSA’s European exposure data put even the heaviest consumers at around 36% of the ADI.
Who needs to avoid aspartame in the UK?
People with phenylketonuria (PKU) must avoid aspartame. UK law requires every aspartame-containing product to carry “contains a source of phenylalanine.” Newborns are screened for PKU on the NHS heel-prick test. The NHS does not restrict aspartame in pregnancy within the ADI; some people choose to limit it by personal preference. For individual guidance, speak to your GP or a registered dietitian.
Where is aspartame used in UK products?
Diet sodas, sugar-free chewing gum, low-calorie yoghurts, sugar-free cordials and squashes, some “diet” cereals, sugar-free sweets, and some sugar-free medicines. UK labelling rules require it to be declared either by name or as E951 in the ingredients list, alongside the phenylalanine warning.
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Sources
- IARC. (2023). IARC Monographs evaluate the carcinogenicity of aspartame, methyleugenol, and isoeugenol. iarc.who.int
- WHO. (2023). Aspartame hazard and risk assessment results released. who.int
- JECFA. (2023). Ninety-sixth meeting -- Summary and Conclusions. Joint FAO/WHO Expert Committee on Food Additives. who.int
- EFSA. (2013). Scientific Opinion on the re-evaluation of aspartame (E 951) as a food additive. EFSA Journal, 11(12), 3496. efsa.europa.eu
- Food Standards Agency. Aspartame. food.gov.uk
- NHS. (2024). Food colours and hyperactivity (includes information on sweeteners). nhs.uk
- Lim U, et al. (2006). Consumption of aspartame-containing beverages and incidence of hematopoietic and brain malignancies. Cancer Epidemiology, Biomarkers & Prevention, 15(9), 1654-1659.
- Debras C, et al. (2022). Artificial sweeteners and cancer risk: Results from the NutriNet-Santé population-based cohort study. PLOS Medicine, 19(3), e1003950.
Last reviewed and updated: 7 May 2026