But high doses are dangerous.

WSJ: Radiation's Effect Depends on Amount

So if this is the case, why did EPA fail to warn their test subjects that the substances they would be exposed to in high doses were so dangerous?

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We already have some pretty good evidence that caffeine, in high doses, can be dangerous, especially for kids and teens.

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Here's a list of herbs and supplements that can be dangerous if taken the wrong way: either in high doses, in combination with certain drugs or before surgery.

CNN: Herbs, vitamins that can hurt you

While he still takes medication the doses are small, and "the evidence shows he is not dangerous", said Hinckley's lawyer, Barry Levine.

BBC: Reagan shooter John Hinckley wants leave from hospital

Low doses, reading some of his writings, seem to be even more dangerous.

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If you haven't received two doses of the MMR vaccine, you are at risk from a disease that can be highly dangerous.

BBC: Swansea measles: Cases rise by 20 to 1,094