I think the trick with ketamine is not so much limiting how much you use in a single day, but rather in not using for many consecutive days in a row. In a study using monkeys, cell death in the brain was noted in monkeys administered injections daily over a period of six months, but not in monkeys administered equal dosages over a period of one month. This indicates that a dosage of ketamine that will not cause permanent brain damage after a single administration could still lead to permanent brain damage if it is repeatedly administered over a prolonged period. I don't think that using a gram in a single day (that is k holing about 5 times for somebody who weighs 200 pounds) is going to cause any long term damage, but maybe if you use a gram a day for 6 months in a row it will.