Can i take st johns wort for low mood while taking gabapentin for neuralgia ( atypical facial - on one side )?

You could: There are no known interactions between st. John's wort and gabapentin, so taking these in combination should not cause a problem. However, it may be helpful to work with a professional regarding your "low mood." st. John's wort can assist with mild-moderate depression, but if more extensive than this may not be effective. Also understanding what's happening before medicating it, seems wise.