I have an issue categorizing my continuous variable. I have put a continuous variable with a negative skew, into three categories. I am using logistic regression and I want to see if my three variables of omega-3 fatty acids will reduce the risk of being in the "psychological distress category" (My dependent variable is 0 - no distress, 1 - psychological distress).

I suspect that when calculating odds rations for the difference between the categories, Stata is using the means of the three categories, and these are being compared against each other and the odds ratio is calculated based on the relative differences between the means of the three categories. This will give me somewhat inflated differences because of the rather extreme values in category three, and I am wondering if I should program Stata to use the medians of the three categories, instead of the mean. Could someone help me get around this?