By Jason McLure

LITTLETON, N.H., June 21 (Reuters) - New Hampshire's Democratic governor on Thursday vetoed a bill passed by the Republican-controlled legislature that would legalize medical marijuana in the state, bucking a trend towards legalization in New England.

Governor John Lynch said the measure did not provide sufficient restrictions on the cultivation and prescription of marijuana. He also opposes provisions authorizing teenagers to use it for treatment.

"I cannot support establishing a system for the use of medical marijuana that poses risks to the patient, lacks adequate oversight and funding, and risks the proliferation of a serious drug," Lynch said.

For the moment, Lynch's move halts the spread of medical marijuana dispensaries in New England.

Maine, Rhode Island, Connecticut and Vermont have all legalized pot for medical use in recent years. Massachusetts voters will decide whether to legalize use in a ballot measure in November.

Nineteen states have passed laws allowing marijuana use for medical purposes.

"The legalization efforts in New England have really been the area that is the most active in recent years," said Keith Stroup, legal counsel at the National Organization for the Reform of Marijuana Laws.

The New Hampshire bill passed by a more than 2 to 1 margin in the state House of Representatives this year, but only narrowly passed the Senate, making prospects for a veto override unlikely. (Editing by Barbara Goldberg and Xavier Briand)

PHOTO GALLERY Legal Marijuana Across The U.S.