By law, the manufacturer is responsible for ensuring that their dietary supplement products are safe before they are marketed. Unlike drug products that must be proven safe and effective for their intended use before marketing.
It is a legal requirement that all nutritional supplements must state what is contained in them, including inactive ingredients, and the amount stated in the correct unit of measurement.
Nutritional supplements have sub-therapeutic and toxic doses, they can cause adverse reactions and interactions with other medication.
People most likely to suffer from an adverse reaction to a nutritional supplement are the same as those who are at greater risk of adverse reaction to pharmaceutical medication such as: the elderly, atopy, compromised liver or kidney function, anxiety or depression, serious illness or those on other medication (Braun and Cohen 2005).
If toxic is associated with causing death or a serious adverse reaction then only some nutrients are of concern. e.g. vitamin A and D and iron. The effects would be dose related.
According to the Lancet, (Palmer et al, July 2003) a third of adverse events associated with dietary supplements were of greater than mild severity. Both new and previously reported associations included: myocardial infarction, liver failure, bleeding, seizures, and death. Increased symptom severity was associated withthe use of several ingredients, long-term use, and age.