Missouri is likely to have 192 medical-marijuana dispensaries by 2020, backers of Amendment 2 said Thursday in a conference call for news outlets.

But, they said, anyone who doesn't possess a "qualifying patient card" for medical cannabis won't be allowed to set foot inside.

New Approach Missouri spokesman Jack Cardetti said the Show-Me State's medical-marijuana system was modeled in part on medical marijuana laws in Colorado and Oregon, "when they just strictly had a medical-marijuana law."

More:Missouri voters have spoken on medical marijuana. They chose Amendment 2.

"They were very effective," he said. In both of those states, about 2 percent of residents had a qualifying patient card to access marijuana for medicinal purposes.

New Approach used that figure to calculate the number of medical marijuana licenses for patients and businesses that it believed Missouri would need.

Thus, each of Missouri's eight congressional districts will be allowed a minimum of 24 dispensaries under Amendment 2.

"We don’t want to have patients having to drive across the state," Cardetti said. "We want it to be close by."

More:All about Amendment 2, the medical marijuana proposal approved in Missouri on Tuesday

Local communities may regulate dispensary locations through existing planning-and-zoning law that covers "time, place and manner," Cardetti said.

That means municipalities or counties can't ban dispensaries, he said.

The state will also issue at least 61 licenses to cultivate marijuana, which works out to 1 cultivator license per 100,000 Missouri residents.

At least 82 licenses will be issued to makers of "marijuana-infused products" like edibles, vapors and oils.

More:When can I get my medical marijuana 'prescription'? A timeline for Amendment 2.

Missouri's Department of Health and Senior Services will issue those licenses, according to the mandates laid out in the amendment.

Over time, Cardetti said, the department can increase the number of licenses to accommodate growth in the number of patients.

Both Cardetti and New Approach campaign manager John Payne said they expected that the Missouri Department of Health and Senior Services will roll out the amendment in a timely manner.

They said part of their intent was to give Missouri's health department "several months" for the rule-making process. They also believe application fees for cultivation and dispensary licenses will give the health department enough funding to bring on staff.

"We worked really hard on making sure the system had enough money to be up and running and we wouldn't have to go to the legislature to appropriate money," Cardetti said.

More:How will Missouri police deal with the new marijuana law? Local law enforcement concerned

In a statement sent to the News-Leader Thursday, Gov. Mike Parson indicated his administration will make medical marijuana happen.

He said, "The people of Missouri have voted to adopt Constitutional Amendment 2, approving medical marijuana. As governor, it is my job to ensure successful implementation of the people’s will. We will begin the very detailed process of implementing a process that makes medical marijuana available to qualified patients."

As the News-Leader reported Wednesday, by law, Amendment 2 "technically" takes effect Dec. 6. By early June, the amendment says, the state health department must be ready to issue medical marijuana applications for patients, caregivers, cultivators, testing facilities, dispensaries, and infused-products manufacturers.

In July, the state should begin taking license applications from patients; in August, it must begin taking applications from would-be operators of dispensaries and the other commercial functions.

More:Guns and medical marijuana: You can't have both, despite Amendment 2

"These are all timelines that require the Missouri Department of Health to act," Cardetti said. "They could certainly move quicker."

Cardetti and Payne emphasized several other key points about Amendment 2.

Public use of marijuana is prohibited. So is driving under the influence of marijuana. Patients with qualifying cards should keep them on their person at all times, Cardetti said.

Patients must be 18 or older, except in special circumstances laid out in the amendment. Caregivers must be 21 or older. They may grow plants at home — up to six for patients; 18 for caregivers — but those must be under "lock and key" and subject to inspection by the Missouri health department.

The amendment lists specific health problems that allow for a doctor to sign off on a qualifying patient card:

Cancer

Epilepsy

Glaucoma

Intractable migraines unresponsive to other treatment

Chronic medical conditions causing "severe, persistent pain or persistent muscle spasms including but not limited to those associated with multiple sclerosis, seizures, Parkinson's disease and Tourette's syndrome"

"Debilitating psychiatric disorders, including but not limited to PTSD" — if diagnosed by a licensed psychiatrist

HIV/AIDS

The amendment also allows leeway for doctors and patients, permitting medical marijuana for the following:

"A chronic medical condition that is normally treated with a prescription medication that could lead to physical or psychological dependence, when a physician determines that medical use of marijuana could be effective in treating that condition and would serve as a safer alternative to the prescription medication;

"Any terminal illness; or

"In the professional (judgment) of a physician, any other chronic, debilitating or other medical condition"

Missouri doctors are not required to recommend medical cannabis for patients who ask for it. "It allows doctors to do so," Cardetti said. "It in no way requires state-licensed physicians to recommend it to patients."

The state health department is expected to play a key role in educating doctors about medical marijuana, he said.

Only Missouri residents will able to apply for a qualifying patient card, but Amendment 2 "does allow for reciprocity for patients with cards from other states to be protected from arrest and prosecution if they come to Missouri with those cards," said Payne, the Amendment 2 campaign manager.

More:Springfield voters sound off on three 'somewhat confusing' medical marijuana votes

Furthermore, a Missouri qualifying patient card will only protect a cardholder in Missouri, unless other states have reciprocity written into their laws or constitutional amendments.

They also noted that under federal budget language passed by Congress in 2014, the Justice Department is prohibited from expending funds toward "going after medical marijuana states," in Payne's words, even though the plant is classified as a schedule I drug and thus illegal under federal law.

A 2013 Justice Department document called the Cole Memo lays out conditions by which medical-marijuana states can remain in the federal government's good graces.

For example, Payne said, marijuana must be produced and processed within a state's borders, and a state may not produce too much marijuana, i.e., "way more product than you'd ever have patients for."

On Wednesday, the News-Leader reached out to the Drug Policy Alliance, a national group that supported Amendment 2, to learn about how Missouri's planned rollout of medical marijuana compares with the 30 other states that have it.

"We've seen completely different implementation timelines," California-based staff attorney Jolene Forman said. "It really depends on how the law is written. Amendment 2 is pretty clear on how it should be implemented."

Forman noted that Amendment 2 was "by far the most popular candidate or issue this election" in Missouri, which creates "political protections because it's so popular."

Amendment 2 was approved by 65.54 percent, with 1,572,592 votes, according to election data collected by the News-Leader.

Along with Missouri, Michigan and Utah voted to ease restrictions on cannabis Tuesday.

USA TODAY Network coverage:Legal marijuana in Michigan: What you need to know

More:Marijuana legalized in Michigan, but group plans to keep fighting it