Bitter almond has been known as laxative in traditional medicine. However, there is no report based on scientific methodology in this regard. In order to assess the possible laxative and prokinetic effects of bitter almond: 1- two groups of 7 rats were gavaged with ethanol extract of bitter almond (500mg/kg) or placebo and were regarded as the test and control groups respectively. Thereafter, the number of feces and fecal weight and percentage of water were studied up to 24h. 2- In order to assess the possible osmotic infiltration of fluids into the intestinal lumen, the jejunum in anesthetized rats (n=5; pentobarbital sodium: 60mg/kg) was randomly divided into 4cm segments and 0.3ml of ethanol extract of bitter almond (125 or 250mg/ml), lactulose (as positive control) or placebo (as negative control) was injected in each segment. The volumes of the contents in each segment were measured after 1h. 3- In order to assess the gastrointestinal transit time, rats were deprived from food and were gavaged with either the extract (250mg/kg, twice with 18h interval) or placebo. Thirty min following the last medication, all rats were gavaged with phenol red and methyl cellulose (1.5ml). Test and control rats, in groups of 3, were sacrificed at times 30min, 1, 2 and 4h, and the amounts of the phenol red in various parts of the gastrointestinal tract were measured. Ethanol extract of bitter almond at a dose of 500mg/kg had a biphasic laxative effect (significantly reduced feces number up to 18h while significantly increased fecal weight and water between 18-24h). It had no significant effects on the osmotic infiltration of fluid into the intestine or on the transit time of the contents in different parts of the gastrointestinal tract. The current results suggest that bitter almond has a biphasic laxative effect that, at least in the used doses, is not mediated via osmotic infiltration of fluids, and that transit time of gastrointestinal contents is not affected.

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