I am convinced that they do. There are times that, once I hit the trail, a relief type calm comes over me and I feel connected to nature.....like I belong in some strange way. After the run I usually feel all around good even if I have had a hard workout and am tired. Trail running relaxes me and that is the time when I can let go of the crazy happenings of life and give my mind a rest. Isn't that why people use drugs and alchohol in the first place, to escape the hectic responsibilities of the world? Running does that as it allows a separation from our demanding lives. We still have to have a balance though as running can be as much of an addiction as any drug.