NOAEL and LOAEL are the upper and lower limits that describe a drug, chemical, vitamin or mineral’s effect on the body. NOAEL is the highest level that seems to have no bad effects. NOAEL stands for No Observable Adverse Effect. LOAEL is the lowest dose level at which bad effects are seen. LOAEL stands for Lowest Observable Adverse Effect Level. These terms are unrelated to the benefits of a substance, they merely determine the range when it may be safe to use.
Establish precise values for NOAEL and LOAEL experimentally. This may not always be possible or ethical, but it is only way to get accurate values. Sometimes these levels can be found from accidental doses, but it would be improper to give, for example, increasing doses of a substance while testing for adverse effects to determine LOAEL.
List the LOAEL for a substance as “none established” if large amounts of the substances seem to have no adverse effects. An example of this is vitamin C. Excessive amounts of vitamin C are eliminated from the body in urine.
Apply one of two rules of convenience that are commonly used by experimenters. When experimentation is impossible and a substance is not known to be toxic at any reasonable level, there are two simple methods to relate NOAEL and LOAEL. The first of these is to consider NOAEL to be one-half of LOAEL. If you look in a table, you will see several instances of this.
Use a statistical method to determine NOAEL and LOAEL. Administer the drug in increasing doses until there is any adverse reaction by anyone to get the NOAEL. Mark the point where the adverse reaction appears in 25 percent of the subjects as the LOAEL.