The main effects of excessive amounts of fluoride consumption are those of dental fluorosis; this affects the teeth (espescially in children where the teeth are still developing) and results in discolouration and brown staining. In very high amounts, fluorides can cause skeletal fluorosis, and this affects the bones, making them brittle. Again, it has a bigger effect on children whose bones have not finished growing. There can also be effects on the kidneys in very high doses.
There is no evidence to suggest that it is carcinogenic (ie, cancer causing). In some parts of the world drinking water naturally contains extremely high levels of fluorides (coming from rocks). The effects are those noted above.
Such excessive doses are almost impossible to achieve, even in areas with fluoridated water. You'd have to be spreading toothpaste on your toast - not just ingesting the occasional tiny bit.
If you're really worried change the paste - but non-fluoride pastes are just as likely to cause gastric problems if you eat a lot, because the main culprit isn't the fluoride. The amounts are really tiny.
