Saccharin
A synthetic sweetener, around 300 to 500 times sweeter than sugar, used in low-calorie and sugar-free products since the early 1900s.
Animal studies at high doses produced bladder tumours, though the mechanism is considered not to apply to humans. Emerging research links regular intake to changes in gut bacteria composition.
What is it?
Saccharin is a non-nutritive synthetic sweetener derived from toluene or phthalic anhydride. It provides no calories and is not metabolised by the body. On labels it appears as saccharin, sodium saccharin, potassium saccharin or calcium saccharin, or simply as E954.
What does it do?
It binds to sweet taste receptors on the tongue far more powerfully than sucrose, delivering intense sweetness with no energy contribution. Because it is not digested or absorbed it passes through the body largely unchanged.
Where you will see it
Tabletop sweetener tablets and sachets, diet soft drinks, sugar-free squash and cordials, low-calorie jams and preserves, sugar-free chewing gum, some pharmaceutical syrups and toothpaste. On UK labels it will appear as saccharin, sodium saccharin, calcium saccharin or E954.
What the science says
Bladder tumours in rats, and why IARC changed its classification
High-dose saccharin feeding caused bladder tumours in male rats in studies from the 1970s and 1980s. However, subsequent research showed the mechanism depends on a precipitation reaction unique to rat urine chemistry that does not occur in human urine. On the basis of this mechanistic evidence, IARC reclassified saccharin from Group 2B (possibly carcinogenic to humans) to Group 3 (not classifiable as to its carcinogenicity to humans) in Volume 73, published in 1999. Large epidemiological studies in humans have not found a clear association between saccharin consumption and bladder cancer.
Saccharin produces bladder tumours in male rats at high doses, but the mechanism involves a rat-specific urine chemistry that is not considered relevant to humans.
IARC reclassified saccharin to Group 3 (not classifiable as to its carcinogenicity to humans), noting the rat bladder tumour mechanism does not translate to human biology.
Two large case-control studies found small elevated risks in certain population subgroups, but results were inconsistent between studies and no clear association was established.
Gut microbiome disruption
Several studies have found that saccharin can alter the composition of gut bacteria even within a week of regular consumption. A 2022 randomised controlled trial found that saccharin consumption raised blood glucose responses to a standard meal in some participants, possibly via changes in gut microbiota. The effect was not universal and depended on individual baseline gut bacteria profiles. This area of research is active but not settled.
Saccharin consumption altered gut microbiome composition and, in a subset of participants, impaired glucose tolerance in a short-term randomised trial.
Earlier mouse studies found saccharin drove dysbiosis and reduced glucose tolerance, effects reversed by antibiotic treatment, pointing to a microbiome-mediated pathway.
2024 EFSA re-evaluation and new ADI
EFSA completed a full re-evaluation of saccharin in 2024 and set a new acceptable daily intake of 9 mg per kilogram of body weight per day. EFSA also recommended that manufacturing remain restricted to the Remsen-Fahlberg synthesis route to control impurities. Typical dietary exposure in European consumers was found to be well below this figure in most population groups, though high consumers of multiple sweetener-containing products may approach it.
EFSA set an ADI of 9 mg/kg bw/day for saccharin and its salts following a systematic review of the available evidence.
Historical cancer warning in the United States
From 1977 onwards, saccharin carried a mandatory cancer warning label in the United States following the rat bladder tumour findings. In 2000, following IARC's reassessment and a review by the US National Toxicology Program, saccharin was formally delisted from the US Report on Carcinogens and the warning label requirement was removed.
Saccharin was delisted from the US National Toxicology Program Report on Carcinogens after the rat tumour mechanism was found not applicable to humans.
Where it stands with the regulators
Who should be careful
People with phenylketonuria do not need to avoid saccharin (unlike aspartame), but should check labels generally. Those monitoring multiple sweetener-containing products in their diet may wish to track intake if consuming large quantities. Look for E954, saccharin, sodium saccharin or calcium saccharin on the ingredients list.
The honest read
Saccharin has had one of the more dramatic scientific reversals in food additive history: widely feared as a cancer risk in the 1970s and 1980s, its warning labels were removed once the rat tumour mechanism was shown not to work the same way in human biology. Human epidemiological studies have not established a bladder cancer link. The open question now is the gut microbiome finding: a 2022 randomised trial found measurable changes in blood sugar response in some participants after saccharin consumption, mediated by shifts in gut bacteria. That finding is real but early, the effect was not universal, and long-term implications are unknown. The science is not settled on this point.
Related additives
Common questions
Is E954 banned in the UK?
No. Saccharin is an approved food additive in the UK and EU, listed on the UK FSA approved-additives register and permitted under assimilated EU Regulation 1333/2008. It can be used in specific food categories up to set maximum levels.
Does saccharin cause cancer?
High doses caused bladder tumours in male rats in 1970s studies, leading IARC to classify it as possibly carcinogenic (Group 2B) in 1980. IARC downgraded it to Group 3 (not classifiable as to its carcinogenicity to humans) in 1999 (Volume 73) after the rat mechanism was found not to apply to human biology. Large human studies have not found a clear link to bladder cancer, and the US removed it from its list of suspected carcinogens in 2000.
What foods contain E954?
Saccharin appears mainly in tabletop sweetener tablets, diet soft drinks, sugar-free squash and cordials, low-calorie jams, sugar-free chewing gum, and some pharmaceutical syrups. It is often combined with other sweeteners. Look for E954, saccharin, sodium saccharin or calcium saccharin on the label.
Is E954 vegan?
Yes. Saccharin is a synthetic chemical compound with no animal-derived ingredients in its production. It is suitable for vegans and vegetarians.
Sources
- UK FSA Approved Additives and E Numbers
- EFSA re-evaluation of saccharin and its sodium, potassium and calcium salts (E 954) as food additives, EFSA Journal 2024
- IARC Monographs Volume 73 (1999): Saccharin and its salts, NCBI Bookshelf
- IARC Summary and Evaluation, Volume 73, 1999: Saccharin and its salts (inchem.org)
- US National Cancer Institute: Artificial Sweeteners and Cancer
- Suez et al., Artificial sweeteners induce glucose intolerance by altering the gut microbiota, Nature 2014
- Suez et al., Personalized microbiome-driven effects of non-nutritive sweeteners on human glucose tolerance, Cell 2022
- US National Toxicology Program: Saccharin delisting from Report on Carcinogens (2000)
Aaron Keen is the founder of NutraSafe. He researches and writes every additive entry himself, from the primary sources. About the research →
This is a guide, not medical advice. If an additive affects you, speak to your GP or a dietitian.
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