VANCOUVER -- A Federal Court judge has struck down the law barring medical users from obtaining marijuana outside of licensed producers, saying it violates their charter rights. Here's a look at medical marijuana:

How many people use it?

About 28,000 people held licences under the old regime and are covered by a court injunction that allows them to grow their own marijuana until Wednesday's Federal Court decision.

What are the rules for obtaining it?

Dried marijuana is not an approved drug or medicine in Canada. However, the courts say people should be provided reasonable access to legal sources for medical purposes. Health Canada requires a health-care practitioner to set out the daily amount of pot required. Individuals can then register with a licensed producer.

Where can it be obtained?

Under the legislation struck down by the Federal Court, it is illegal for producers to provide medical pot through a storefront, compassion club or dispensary. However, the government has authorized 29 medical producers to distribute medical pot to registered patients. The producer is required to securely ship pot directly to either the patient, an individual responsible for the patient, or to the patient's health-care practitioner.

How much pot can be obtained?

Patients are allowed to possess a maximum of 30 times the daily amount identified by their health-care practitioner, or 150 grams, whichever is less. Authorized producers may only provide dried marijuana, fresh marijuana or cannabis oil.

Who produces medical marijuana?

A total of 29 producers are licensed by the federal government: 16 in Ontario, seven in British Columbia, two in Saskatchewan and one each in New Brunswick, Quebec, Manitoba and Alberta.

Some of Canada's biggest producers include Canopy Growth Corp., the parent group of Tweed Inc., Bedrocan Canada Inc., and Mettrum Ltd. Ontario-based Tweed Farms is housed in a former Hershey Chocolate factory, where it is licensed to grow cannabis plants in its 32,516 square-metre greenhouse and sell 3,500 kilograms of dried cannabis, Canopy Growth says.

Are there any storefront marijuana retailers?

Although marijuana retailers have opened across British Columbia, including more than 100 in Vancouver and 26 in Victoria, they remain illegal. However, the City of Vancouver has introduced a bylaw to regulate the stores and more than a dozen applicants have so far progressed through the stages of licensing.

What does research say about the effectiveness of medical pot?

The Canadian Centre on Substance Abuse says there is "sound evidence" from animal experiments and clinical trials involving humans that marijuana is effective for the relief of nausea, vomiting, certain types of pain, and the stimulation of appetite.

Some specific therapies include relieving vomiting caused by anticancer chemotherapy, stimulating appetite in AIDS patients and relieving pain related to multiple sclerosis and advanced cancer.

The centre found a lack of research examining the risks of medical marijuana, although states that studies of recreational users shows health risks related to smoking pot over the long term. It says no research to date has investigated the risks marijuana dependence, in the context of long-term supervised medical use.