The side-effects of a new sustained release oral ferrous sulphate preparation have been evaluated in three separate double-blind studies. Each tablet contained 100 mg of ferrous iron and the dosage employed in all studies was 2 tablets daily.

In a large series of blood donors randomly divided into three groups the frequency and type of side-effects were compared to ferrous sulphate tablets and placebo.

In two series of pregnant women the side-effects were studied with a cross-over technique using ferrous sulphate tablets as reference. Placebo was also included as a reference in one of these studies.

In all series the frequency of nausea and epigastric pain was about the same for the sustained release preparation as for placebo. In all series ferrous sulphate tablets gave a significantly higher frequency of nausea than the sustained release tablets and placebo. Also the frequency of epigastric pain was found to be higher in blood donors but this could not be verified in pregnant women.