aspartame as “possibly carcinogenic to humans,” Group 2B. From the American Cancer Society: "It’s important to know that IARC classifications are based on the strength of the evidence of whether something can cause cancer in humans, not how likely it is to cause cancer. The Group 2B classification is the third highest out of 4 levels, and it is generally used either when there is limited, but not convincing, evidence for cancer in humans, or when there is convincing evidence for cancer in lab animals, but not both."