Aspartame (E951): What It Is and What the Evidence Says

Aspartame is an intense, low-calorie sweetener. Its European additive number is E951. EFSA describes aspartame as approximately 200 times sweeter than sugar. Because it is so sweet, relatively small quantities can provide the sweetness required in a food or drink.

In Europe, aspartame is authorised for use in specified food categories, including products such as certain drinks, desserts, sweets, dairy products, chewing gum and tabletop sweeteners.

So when you see Sweetener: aspartame or Sweetener: E951, you're looking at the same additive. More on how the system works in our guide to E numbers.

There are specific labelling rules. Food containing an authorised sweetener must generally carry with sweetener(s) near the name of the food. If the product contains both added sugar and a sweetener, the wording is generally with sugar(s) and sweetener(s).

Aspartame has an additional requirement because it is a source of phenylalanine. FSAI explains that where aspartame is listed only by its E number, the label must state contains aspartame (a source of phenylalanine). Where it is listed by its specific name, the required wording is contains a source of phenylalanine.

These statements are particularly important for people with phenylketonuria, or PKU. See also how to read an ingredients list.

The current Acceptable Daily Intake, or ADI, for aspartame is 0–40 mg per kilogram of body weight per day. An ADI is an estimate of the amount of a substance that can be consumed daily over a lifetime without presenting an appreciable health risk, based on the available evidence.

It is not a recommended amount to consume. And it isn't the point at which one extra milligram suddenly causes harm. It's a long-term safety benchmark used in risk assessment.

EFSA's 2013 full re-evaluation retained the 40 mg/kg body-weight ADI and concluded that estimated consumer exposure was below it. Importantly, that number is still current. In September 2026, EFSA reassessed newer evidence while evaluating the related sweetener E962, the salt of aspartame-acesulfame, and reconfirmed the existing 40 mg/kg body-weight ADI for aspartame.

This is where most of the confusion comes from. In July 2023, the International Agency for Research on Cancer, or IARC, classified aspartame as possibly carcinogenic to humans, Group 2B. IARC said there was limited evidence for carcinogenicity in humans.

At the same time, the Joint FAO/WHO Expert Committee on Food Additives, or JECFA, completed its own assessment. JECFA concluded that the evidence did not provide sufficient reason to change the existing ADI and retained 0–40 mg/kg body weight per day.

Those findings can look contradictory. They're answering different questions.

IARC uses several hazard categories. Group 2B means possibly carcinogenic to humans. The classification reflects the evidence available for a potential cancer hazard. It is not a ranking of how dangerous everyday exposure is, and it doesn't tell you how much exposure someone would need before risk changes.

In its 2023 evaluation, IARC described the evidence for carcinogenicity in humans as limited. That's important context. The responsible interpretation isn't that WHO proved aspartame causes cancer. That isn't what happened. It's also not useful to pretend the IARC classification doesn't exist.

IARC identified a possible hazard based on limited evidence, while JECFA separately assessed exposure and retained the established ADI.

No. Safety assessment and dietary strategy are different questions. A food additive can be authorised within established intake limits without being something you need to actively include in your diet.

Likewise, reducing sugar using a sweetener can substantially alter the sugar and energy content of a product without automatically making that product nutritionally complete. So rather than asking only "aspartame: safe or unsafe?", it can be more useful to ask:

This is where study design matters. Observational research can identify associations between dietary exposure and health outcomes. Those studies can be important. But an association does not automatically establish that one ingredient caused the outcome. Researchers have to consider issues such as:

• other dietary differences
• lifestyle
• existing health conditions
• measurement error
• reverse causation
• other confounding factors

This doesn't mean observational evidence should be dismissed. It means claims should match what the study design can actually establish. That's one reason regulatory assessments generally consider multiple types of evidence together, rather than drawing conclusions from a single study.

Sláinte is designed to make this interpretation easier without turning one ingredient into the whole verdict. If a label contains E951, Sláinte can identify it as aspartame and explain that it is a sweetener. The ingredient is then considered alongside the wider product.

As of 2 October 2026, the live Sláinte methodology weights food scores as follows. It also applies a published guardrail that prevents artificially sweetened products from scoring above 74, meaning they cannot enter the Excellent band.

That is a Sláinte scoring decision. It should not be confused with an EFSA or WHO safety threshold. The point of the score is to consider the product across several dimensions rather than allowing one characteristic, whether positive or negative, to determine the entire result. See also common food additives.