"I believe the effort to try and make marijuana available for medical uses is really a way to legalize it. There's no reason for it," the former New York mayor said during a town hall-style meeting at New Hampshire Technical Institute.
He also said there are better alternatives.
"You can accomplish everything you want to accomplish with things other than marijuana, probably better. There are pain medications much superior to marijuana," he said.
"We'd be much better off telling people the truth. Marijuana adds nothing to the array of legal medications and prescription medications that are available for pain relief."
After a speech at the first of several stops in the first-primary state, the early front-runner in the race for the Republican nomination fielded questions. None dealt with the unpopular war in Iraq.
Instead, voters wanted to know about the failed immigration bill and Giuliani's views on climate change and health care.
Giuliani said promises of universal health care are hollow and simply not manageable.
"If you try to do socialized medicine, a la Hillary Clinton, John Edwards, Barack Obama or Michael Moore, you're going to end up with a disaster," he said.
He urged voters to press other candidates for specifics and to move beyond lofty language.
"We tried that before. We tried that with the `War on Poverty' and we tried that with welfare. Look what happened. We tried a simplistic solution and look what happened. We locked people into poverty. It was a tragedy."