3.5 would have me sick and near nodding, being opiate naive (and smoking weed all the time, that seems to have an adverse effect as well, just thought I'd mention it). I'd start with ~2 if it's good, depends on the batches too, not one of them is the same really. You can always add a little more, but the first times I was adviced ~3 grams, it had me so sick and depressed, lol, that painted my whole kratom experiences for over a long time.