Amounts found in supplements (5–20 mg) have not been linked with any toxicity. Excessive intake of manganese rarely lead to psychiatric symptoms. However, most reports of manganese toxicity in otherwise healthy people have been in those people who chronically inhaled manganese dust at their jobs e.g., miners or alloy plant workers. Other sources of manganese intoxication are now recognised, including total parenteral nutrition (TPN) in patients who are being fed intravenously^{6, 7, 8} and pesticides containing manganese in agricultural workers who have been exposed.⁹

Preliminary research suggests that people with cirrhosis¹⁰ or cholestasis (blocked bile flow from the gall bladder)¹¹ may not be able to properly excrete manganese. Until more is known, these people should not supplement manganese. Manganese supplementation (3–5 mg per day) has caused severe hypoglycaemia (low blood sugar) in a person with insulin-dependent diabetes.¹² People with diabetes who want to take manganese should consult their doctor.