any amount that is deemed needed by the caregiver or patient is legal, but watch out over 100 and they call the feds in on you.
this is a direct quote from the amendment
(4) (a) A patient may engage in the medical use of marijuana, with no more marijuana than is medically necessary to address a debilitating medical condition. A patient's medical use of marijuana, within the following limits, is lawful:

(I) No more than two ounces of a usable form of marijuana; and

(II) No more than six marijuana plants, with three or fewer being mature, flowering plants that are producing a usable form of marijuana.

(b) For quantities of marijuana in excess of these amounts, a patient or his or her primary care-giver may raise as an affirmative defense to charges of violation of state law that such greater amounts were medically necessary to address the patient's debilitating medical condition.