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No Observed Adverse Effect Level

Similar term(s): NOAEL, NOEL (no observed effect level).

The highest tested dose of a substance that has been reported to have no harmful (adverse) health effects on people or animals.

Source: ATSDR Glossary of Terms  

Can apply to a particular study, species (e.g. rat, dog), or all studies on a particular substance. The difference between NOAEL and NOEL rests on the definition of adverse effect only, that is, an experimental study that produced a NOAEL will have stated the adverse effect to be observed before initiation.

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