Hampered detoxification processes can result in a condition labeled by many naturopathic and nutrition-oriented physicians as the "congested" or "sluggish" liver, or the more recently coined "impaired hepatic detoxification". Standard liver enzyme blood tests may or may not be elevated in such cases. The congested or sluggish liver is characterized by a diminished bile flow, a condition known in medical terms as cholestasis, while impaired hepatic detoxification refers to decreased phase I and/or phase II enzyme activity. Phase I detoxification rates that are in excess of phase II activity will also cause toxicity problems due to excessive accumulation of activated intermediates. Although there are more sensitive tests to determine the functional activity of the liver, such as a serum bile acid assay and various clearance tests, clinical judgment based on medical history remains the major diagnostic tool for the sluggish liver. The presence of chronic fatigue is a frequent symptom. Clearance tests using saliva, urine, and/or blood after chemical challenge by caffeine, aspirin, and acetaminophen can be useful in detecting Phase I and II imbalances.

Impaired liver function can result from intrahepatic problems caused by exposure to food additives, solvents (cleaning materials, formaldehyde, toluene, benzene, etc.), pesticides, herbicides, heavy metals (lead, mercury, cadmium, arsenic, nickel, and aluminum), and other toxins. Other causes include viral infections of the liver, some inherited disorders such as Gilbert's syndrome, alcohol induced fatty deposits, the use of anabolic steroids/estrogens/oral contraceptives and hyperthyroidism. Bile flow can be restricted also by extrahepatic means such as gallstones, pregnancy, or other physical causes such as tumors.

Among the other symptoms, people with a sluggish liver may complain of depression, general malaise, headaches, digestive disturbances, allergies and chemical sensitivities, premenstrual syndrome, and constipation. Not surprisingly, these are the same types of symptoms people exposed to toxic chemicals often complain of. Many toxic chemicals (especially solvents) and heavy metals have an affinity for nervous tissue, giving rise to a variety of psychological and neurological symptoms such as depression, headaches, mental confusion, mental illness, tingling in extremities, abnormal nerve reflexes, and other signs of impaired nervous system function.

The capacity of the liver to detoxify any given compound is determined not only by the inherent toxicity of the compound but also by the available supply of nutrients and endogenous molecules required for Phase I and II reactions, by any pre-existing liver disease which may be present and by the total load of all toxins to which it is exposed.