Healthy individuals who already eat a balanced diet but also take multivitamins could be spending money unnecessarily, an investigation by Choice found.
Although there is sometimes clinical evidence to support taking a supplement, the doses can often be way below levels required to have a significant impact, the organisation said.
"If you have a healthy diet and you're not a person with specific nutritional requirements, there's a good chance you're wasting your money," Choice spokeswoman Ingrid Just said.
"At 20 to 70 cents per day for multivitamin products we priced, the 'worried well' can spend several hundred dollars a year simply by taking a daily pill.
"Marketing messages, often backed up by high-profile sporting celebrities, give the impression that we all need multivitamins to be fit and healthy," she said in a statement.
People taking a range of multivitamins without checking the recommended daily intake (RDI) requirements could be exceeding the RDI for some vitamins and potentially putting their health at risk, as not all vitamins are safe in high doses.
But most multivitamins contain lower doses of ingredients so it's harder for them to be over-consumed, the investigation found.
Vitamin labelling could also confuse consumers, with some labels stating the vitamin name such as B3, while others using the chemical name, niacin.
"An untrained person probably wouldn't know that the two things are one and the same," Ms Just said.
Manufacturers of products sold in Australia are not required to list how each ingredient amount relates to RDI.
"We want manufacturers to list vitamin and mineral values according to the percentage of an appropriate RDI in each dose to help consumers compare apples with apples," Choice's investigation concluded.
Multivitamins are big business, with Choice identifying eight different multivitamin products marketed by both Blackmores and Nature's Own, 11 by Nature's Way and 16 by Swisse.
But some groups definitely benefit from supplements, including pregnant women taking folate before and after conception, the study pointed out.
Choice recommends individuals consult a dietician or GP about their nutritional needs before opting for multivitamin or other supplements.