SEATTLE (AP) – In one corner of Washington state, a 62-year-old rheumatoid arthritis patient could face more than eight years in prison for growing marijuana for himself and three others. In Seattle, meanwhile, a collection of grow operations serves 2,000 people with little interference from police.

The discrepancy is typical of the confusion that has reigned since voters passed Washington's medical marijuana law more than a decade ago. Nor have things improved much since the state clarified how much pot patients can have last year.

Unlike some states, Washington requires patients to grow marijuana themselves or designate a caregiver to grow it for them. For many, that's unrealistic: They're too sick to grow cannabis themselves and don't have the thousands of dollars it can cost for a caregiver to set up a proper growing operation.

So they've devised their own schemes, claiming to meet the letter of the law in establishing collective grows or storefront dispensaries – methods that are making police and prosecutors increasingly uncomfortable.

"The spirit of the law would recognise the necessity of having small cooperative ventures," said Dan Satterberg, the prosecutor in King County, where Seattle is. "But if they get past a certain size, become a magnet for neighbourhood violence, or you get other people showing up to buy marijuana who are not permitted to under the law, then there's tension."

Three years ago, Satterberg's office declined to prosecute a man who was growing 130 plants for 40 people. But a case this year may be testing his tolerance: He hasn't decided whether to charge a hepatitis patient caught with 200 plants, which he claimed supplied more than 100 other patients.

Some activists and the American Civil Liberties Union of Washington recently began discussions with Seattle police over whether to limit the size of cooperative grows.

In Spokane this month, police shut down a medical marijuana dispensary – the first such bust in the state – and arrested the two owners. They warned a half-dozen other dispensaries to close as well, and the raid quickly drew protests from patients. The raid has set up a high-profile court fight. Approved by voters in 1998, it allows doctors to recommend cannabis as a treatment for a series of debilitating or terminal conditions – a smaller range of illnesses than California's law. A year ago, the state issued guidelines to give police and patients alike an idea of how much pot was OK: Up to 15 plants and 24 ounces of dried marijuana per patient. People can have more if they demonstrate need.

Police in some jurisdictions have applied the guidelines strictly, arresting people simply for having more than 15 plants, even if they possessed no usable marijuana. In Seattle, Satterberg issued a memo to law enforcement saying he wasn't interested in dragging sick people to court. Some other counties have also adopted a lenient view.

Washington's law says that a caregiver can only provide marijuana to one patient at any one time. In Spokane this year, medical marijuana activists focused on that language in setting up a for-profit dispensary called Change. Lawyer Frank Cikutovich said the business met legal requirements: A lone patient would enter the store, sign a document designating the shop as his or her caregiver, and buy marijuana. The agreement expired when the patient left and the next customer came in.

The business, raided on September 10, rendered the "one patient, one caregiver" rule meaningless, Spokane police spokeswoman Jennifer DeRuwe said.