The Food and Drug Administration (FDA) in Thailand is looking into substandard prenatal vitamins with varying levels of iodine, and has said that if the problem is found to be a manufacturing error, production would be suspended and all products recalled.

FDA secretary-general Boonchai Somboonsuk said yesterday that the Department of Medical Sciences' initial probe found that 69 per cent of prenatal vitamins, produced domestically or imported, were substandard as the amount of iodine in them was either non-existent or 40 times higher than stated in the label.

So, the FDA will study the findings and check on related details including the manufacturing procedure, transport and storage of the product to determine the cause of the problem, he said.

"The key ingredients of these vitamins are not dangerous, except for iodine levels," he said, adding that only a prolonged intake of excessive iodine can affect the thyroid gland.