Came across this in UK paper:'Male and female brains are fundamentally different in their response to painkillers according to scientists.They have found that an experimental painkiller produces precisely opposite effects in some crucial parts of the brains of female rats from those it produces in the same parts in male rats.Experiments on humans showed that, while the Kappa-opiod drug is effective for women, it can increase pain for men if given in low doses.The findings prove that when drugs are evaluated for use by humans they should be tested separately for use by men and by women, according to researchers from University of california, in the journal Pain.Professor John Levine said; 'People need to understand that male and female brains are different. This fact has to be taken into consideration when thinking about drug treatments, particularly drugs that act on the central nervous system'There may be classes of drugs that are particularly effective in women that don't have the side-effects of available potent drugs. Kappas are an example, but it may be true for a lot of drugs''Interesting.Haven't Kappa-opioids been used in IBS trials?