A snapshot of medical marijuana rules in various states:

Alaska: Patients (or their primary caregivers) may legally possess up to 1 ounce of usable marijuana and may grow up to six plants. There is a confidential state-run patient registry.

Arizona: Doctors are allowed to prescribe marijuana to unspecified "seriously ill" patients. Medical leaders, however, say physicians aren't prescribing the drug because, in part, they fear doing it would put their federal licenses to prescribe drugs at risk. The Arizona Department of Public Safety contends that federal law trumps state law and it remains illegal to grow or distribute pot.

California: People can posses no more than 8 ounces and six mature or 12 immature marijuana plants. Counties and cities are free to permit greater quantities and a larger amount if it is required for the patient's "medical needs." Two dozen cities and counties have various guidelines, with the high end permitting 99 pot plants and several pounds of processed pot. Patients must have an oral or written recommendation from a physician - who cannot be punished for having made such a recommendation - and must have a serious illness such as AIDS, glaucoma or arthritis. However, unspecified other illnesses are permitted if pot provides relief. The law also will set up a voluntary state-run identification card system for users.

Colorado: Patients must have written documentation from a doctor that they suffer from a debilitating condition that marijuana may help. It lists several of them, including cancer, AIDS and chronic nausea, with state health officials authorized to approve others. The law establishes a state-run registry program. The legal limit is 2 ounces of usable marijuana and six plants.

Hawaii: Requires signed statement from a physician and specifies the illnesses covered, including Crohn's disease and epilepsy, with others subject to state approval. Sets up a mandatory state-run patient ID program. Possession limits are 1 ounce of usable marijuana and seven plants.

Maine: Patients must have an oral or written "professional opinion" from their physician that he or she "might benefit from the medical use of marijuana." Names the illnesses. Legal limit per patient or caregiver is 2 1/2 ounces of usable marijuana and six marijuana plants.

Maryland: Allows patients arrested for marijuana-related crimes to argue in court that they need it medicinally. If the judge agrees there is a medical necessity, the maximum penalty allowed by law would be a $100 fine.

Nevada: Patients need a written document from a physician. Lists various permitted illnesses, with others subject to state approval. The legal limit is 1 ounce of usable marijuana and seven marijuana plants. Sets up a state-run ID card program. Patients who do not join the registry or who possess greater amounts of marijuana than allowed by law may argue the "affirmative defense of medical necessity," if they are arrested.

Oregon: Patients must have a signed physician's recommendation and the illnesses covered are listed, including Alzheimer's disease, with other conditions subject to state approval. The limit is 3 ounces of usable marijuana and seven plants. If a patient is arrested, he or she must have been diagnosed by their physicians at least 12 months before the arrest to present a medical marijuana defense. Law enforcement agencies that do seize marijuana plants aren't required to keep them alive.

Vermont: Limit of 2 ounces of usable marijuana and three marijuana plants. Certain illnesses are specified. The law also sets up a state-run registry.

Washington: Patients or their primary caregivers can possess or cultivate no more than a 60-day supply of marijuana. Patients must possess "valid documentation" from their physician. Lists specific illnesses, with others to be approved by the state. Physicians cannot legally prescribe marijuana; they only can advise. Marijuana cannot be legally purchased and there is no identified legal way to distribute it.

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Sources: NORML Foundation, state sources.