Normally, you should not perform one-tailed tests.I have been doing one tailed independent two sample t tests

You make yourself half blind.

If your total sample size is > 50 or so, non-normalbut now on other data I no longer have normal distributions so I wanted to use Mann Whitney U test,

distributions shouldn't matter much. One has to be

more concerened with unequal variances (if samples

have unequal size).

Seems so. But normally you shouldn't do so.do I then divide p/2 as I would for the t test to get a one tailed p value?

With kind regards

K.