NEW YORK (Reuters) - New York's first medical marijuana dispensaries are opening their doors on Thursday, as the state launches one of the most conservative programs of its kind in the United States.

New York joins 22 other states and Washington, D.C., with comprehensive programs that allow the legal use of marijuana by cancer, AIDS and other patients certified by a physician.

The openings in New York come more than a year and a half after Governor Andrew Cuomo signed legislation, known as the Compassionate Care Act, that allow patients to use marijuana to ease their symptoms. Proponents of medical marijuana had advocated for the move for years.

"Our program ensures the availability of pharmaceutical-grade medical marijuana products for certified patients and establishes strict regulatory controls to protect public health and safety,” New York State Health Commissioner Dr. Howard Zucker said in a statement.

Under the program, the state has licensed five organizations to manufacture and sell medical marijuana, with each allowed to operate four dispensaries. All of them are expected to be up and running by the end of the month.

Eight dispensaries across the state are scheduled to open on Thursday, in locations including New York City and Albany, health officials said.

The program is strictly limited to patients with very serious and terminal illnesses, including cancer, HIV and AIDS, Parkinson's disease and epilepsy.

Unlike the all other states that allow medical marijuana, except Minnesota, the program prohibits marijuana for smoking. It only allows the drug to be sold in liquid or oil form for vaporizers and inhalers or capsules taken orally. It also prohibits the cultivation of plants by patients.

In addition, New York requires a four-hour mandatory training course for physicians before they can certify patients, a requirement not mandated by other state programs, according to the National Conference of State Legislatures.

Medical researchers have applauded New York’s conservative approach. They say the state’s tight controls over prescribing, dosing and other aspects of the program will allow for more reliable study of the efficacy of medical marijuana.

“Really, what they're trying to do is close to legitimatize med marijuana,” said Edward M. Bednarczyk, University at Buffalo’s pharmacy practice chair, referring to the approach taken by New York regulators.

But critics say New York has gone too far in limiting in the types of patients allowed in the program and how those who qualify can use the drug.

“At best, it could be seen as a half-step, but not a full step, to embracing the actual medical utility of cannabis,” said Paul Armentano, deputy director of National Organization for the Reform of Marijuana Laws.

(Editing by Frank McGurty and Marguerita Choy)