St. Johns Wart and Melatonion-Reactions???? Side efects??

I have been having great results with St. Johns Wart and take it often to keep myself mentally healthy and to avoid another depressive relapse. Occasionally I have trouble sleeping and a friend suggested that I go to the store and pick up Melatonin which is a sleep support viaminin(This is not a drug or prescription medication/pill but an organic form of sleep support). I was wondering if anyone knows of any possible reactions between the 2 supplements. If it is safe to take the 2 together. Thanks.