In some people the detoxification pathways (Phases I and II) are out of balance. For example, if Phase I is more active than Phase II, a build up of reactive intermediate metabolites can occur which in turn can lead to tissue damage and disease. These people are referred to as "Pathological Detoxifiers".

Pathological detoxifiers can be identified as those individuals who are highly sensitive to fumes e.g. paints and perfumes, react adversely to various pharmaceutical drugs and may have a reaction to drinking caffeine. Testing your detoxification ability is recommended.

However, a person with these reactions may instead be a "Poor Metabolizer". For example, about one person in 12 in the Caucasian population inherits a defective enzyme - CYP2D6 - one of the Phase I enzymes. This enzyme catalyses the metabolism of more than 40 widely used drugs, including antidepressants, cardiovascular agents, analgesics and drugs of abuse such as ecstasy. With some drugs, poor metabolisers may achieve concentrations in their blood as much as 150 times higher than usual after a normal dose, thus producing side effects.

When liver metabolism is out of balance, testing should be done to confirm where the imbalance may be and help determine which nutrients should be taken. Some of these nutrients are listed under the treatment "Liver Detoxification Support".