One can be either an over-methylator or an undermethylator.
Sam-e is great for under-methylators because it provides the building blocks necessary to breakdown excess histamine in the body which is a nervous system irritant. If one has excess histamine in the body the adrenals must produce adrenaline to break it down (this is what en epi-pen does). Over time this can cause adrenal fatigue. Just another one of the litany of possible causes.
I don't think Sam-e would be good for overmethylators though, who suffer from a lack of histamine in the blood, which can also cause problems.
I thought I was an under-methylator. And in fact I may be, a Low Histamine Diet and supplementation with methionine did not make a noticeable difference for me, although increased vitamin C supplementation has helped in general. (Vit C breaks down histamine among other benefits).