From BBC news online.

Thursday, 14 July, 2005, 15:26 GMT 16:26 UK

Sweetener 'linked' to leukaemias

Fresh doubts about the safety of an artificial sweetener have been raised by Italian scientists who have linked its use to leukaemias in rodents.

Aspartame is 200 times sweeter than sugar and is used throughout the world in low-calorie drinks and foods.

Regulators say existing studies show it is safe, but will look at the European Journal of Clinical Oncology study.
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This is from Seize the Day's website. I can't vouch for accuracy but if you doubt them, it's probably checkable.
 http://www.seizetheday.org/monsanto/main.htm
NUTRA-SWEET/ASPARTAME

Aspartame was originally listed in the US military's Chemical Warfare division - whether it was used as a sweetener to hide the taste of poison, or as a poison itself, is not clear.

Now used as an artificial sweetener, it was banned in the USA for causing brain-tumours -

The ban was over-turned under Ronald Reagan.