TALLAHASSEE — Come Nov. 8, Florida could be the 26th state to legalize full-strength medical marijuana for patients with cancer, epilepsy and a host of other conditions.

That gives supporters and opponents of Amendment 2 just five weeks to persuade voters. And they've started in earnest, pumping millions of dollars from wealthy donors into TV ads, mailings and recruiting big-name endorsers.

Pro-medical marijuana group United for Care has logged $5.2 million since 2015, most of it from large donors, including a $1 million contribution last week from pot activist group New Approach.

The biggest donor is Orlando trial lawyer John Morgan, whose firm has spent $2.7 million to get the amendment on the ballot this November and has funded some radio ads statewide. On a similar measure in 2014, Morgan spent $4 million, but he does not intend to be United for Care's sole source of money going forward.

"John's position — and mine too — is, 'I got us here. Let's let other people finish us out,' " said campaign manager Ben Pollara. "Unless I absolutely need it, I'm not asking him for another cash donation."

A poll released last week by the Florida Chamber of Commerce shows 73 percent of likely voters support Amendment 2, well above the 60 percent threshold required to put it in the state Constitution.

But opponents of the amendment are hitting back hard.

A group called Drug Free Florida Committee has already spent more than $1.7 million buying TV advertising, relying on $1 million donations from St. Petersburg developer Mel Sembler and Las Vegas casino magnate Sheldon Adelson.

Their newest ad, released Monday and set to broadcast in all of the state's media markets, says Amendment 2 will allow for "pot packaged like candy … marketed to kids."

On Friday, the group's No on 2 campaign announced support from state Sen. Jack Latvala, R-Clearwater, who faces only a write-in opponent in the general election and is ready to spend "the lion's share" of his campaign funds to defeat Amendment 2. He's starting with a $100,000 ad buy this week in the Tampa Bay area.

"I just see too many opportunities for abuse," said Latvala, who will be the Senate budget chairman next year. "I'm concerned that the Constitution is permanent. I just think that that's a big risk we're talking about with this amendment."

A similar constitutional amendment failed in 2014 with 58 percent support after a contentious fight. The battle brewing this year likely will look familiar.

Opponents have varying concerns: That Florida will see an explosion of pot shops on every corner, state and local lawmakers won't be able to regulate the program and that the issue should be left up to the Legislature, not a constitutional amendment. Some, including Latvala, oppose medical marijuana outright.

In advertising that will begin this week, supporters are likely to showcase stories of sick patients who have been helped by marijuana and families desperate to try the drug as a treatment for loved ones.

Since the 2014 election, a medical marijuana program went into effect in Florida to provide strains of the drug low in THC — the chemical that causes a euphoric high — for some patients, including children with severe epilepsy and cancer. Florida's first low-THC cannabis went on sale in July.

This spring, Gov. Rick Scott signed a law that allows doctors to recommend full-strength medical marijuana for patients within one year of death. It is expected this fall for terminal patients.

Medical pot's supporters hoped the Florida Legislature would pass a broader medical marijuana law. Now, they see Amendment 2 as their best hope.

"Our government has failed its citizens on medical marijuana policy," Amendment 2 backer Sen. Jeff Brandes, R-St. Petersburg, said in a statement. "Today we have a law on the books that enriches a handful of people, and places barriers between doctors and their patients by depriving them access to a treatment that could improve their quality of life."

Contact Michael Auslen at mauslen@tampabay.com. Follow @MichaelAuslen.