(CHICAGO, AP) — Illinois became the 20th state in the nation to allow the medical use of marijuana Thursday, with Gov. Pat Quinn signing some of the nation’s toughest standards into law.

The measure, which takes effect Jan. 1, sets up a four-year pilot program for state-run dispensaries and 22 so-called cultivation centers, where the plants will be grown.

Quinn, a Chicago Democrat, focused his remarks on how medical marijuana will help seriously ill patients, including veterans, which have been a key focus during his time in office.

“It’s very important we do whatever we can to ease their pain,” Quinn said Thursday at a new medical facility at the University of Chicago. “It’s a very well-drafted bill.”

Under the measure, only patients with serious illnesses or diseases will be allowed to obtain medical marijuana. The bill lists more than 30 illnesses, such as cancer, muscular dystrophy and Lupus. The patients must have established relationships with a doctor and will be limited to 2.5 ounces every two weeks.

Currently, 19 other states and Washington, D.C., allow medical marijuana. New Hampshire Gov. Maggie Hassan signed a medical marijuana bill into law last week.

Illinois’ rules are among some of the strictest in the nation, according to Karen O’Keefe, director of state policies at the Marijuana Policy Project. The Washington-D.C. based legalization advocacy group tracks state laws and helps some craft bills.

For one, Illinois won’t allow home growing operations like more than a dozen other states do. The growing centers will have to be under 24-hour video surveillance, which is uncommon compared to other states. O’Keefe said most states also have more general guidelines on who can obtain medical marijuana.

Legalizing medical marijuana faced some opposition in Illinois, mainly from opponents who feared it would encourage drug use and authorities who feared it would complicate driving-under-the-influence tests. Some anti-crime groups also objected to the 2.5-ounce amount, which they said was too much.

Bill sponsor Rep. Lou Lang, dismissed the concerns, saying it would be difficult to obtain the drug for anyone who didn’t need it.

“This was for the patients,” Lang said Thursday. “This was for the state of health care … in Illinois.”

He has also said that the 2.5-ounce amount is to accommodate patients who ingest, not smoke, it, such as baked goods.

“Those folks all they focus is joints,” the Skokie Democrat said of opponents. “Most (patients) don’t smoke it, they cook with it or vaporize it.”

Army veteran Jim Champion was at Thursday’s news conference. He’s suffered from a progressive form of multiple sclerosis for 25 years, leaving him a quadriplegic.

At one time, he was taking nearly 60 pills a day, including morphine and valium. But he said marijuana — which his wife obtained illegally — was the only thing that gave him relief from chronic and constant pain.

“Today I feel vindicated,” the Somonauk man said in an interview. “Patients, many sicker than myself, will have access to a quality product.”