We had unpleasant (but far from unbearable) symptoms briefly every time we increased dose until 3.0 mg. After that we had no problems increasing dose by 0.5 mg weekly until we got up to 4.5 mg. We are not particularly sensitive to meds, so that increase rate may be too much for people who are.
We started noticing positive effects at about 3.0 mg, but we seem to be doing better at 4.5 mg. So for us, full dose (4.5 mg) is best. That could be a very individual thing, though.
So far we have not experienced it ceasing to work, but we are also taking Valcyte atm, which has some affect on microglia, so that could be masking any variation in the effect of LDN.