TRENTON -- Gov. Chris Christie signed a bill into law Wednesday that would add post-traumatic stress disorder to the list of conditions that would qualify people for medical marijuana, a move actively sought by combat veterans.

Christie said he supported the bill because an estimated 20 percent of veterans returning from the Iraq and Afghanistan suffer from this "debilitating" illness.

Other means of treatment would have be tried first before a doctor could recommend cannabis, to prevent "misuse," according to the governor's bill-signing statement.

"The mere potential of abuse by some should not deter the state from taking action that may ease the daily struggles of veterans and others who legitimately suffer from PTSD," Christie wrote.

Christie has been reluctant in the past to broaden admissions to the medical marijuana program. The law creating the program gives the state health commissioner the authority to decide whether new medical conditions should be added to the list. The governor has resisted many attempts to deviate from the law, which he has complained is too lax and a gateway to legalization.

Lawmakers praised his decision.

"I am pleased that Gov. Christie agreed with our legislation that finally empowers doctors to treat veterans and other PTSD patients with this indisputably effective medicine," Sen. Joseph Vitale (D-Middlesex), a lead sponsor of the bill.

"Veterans - especially post-9/11 veterans - are the group most affected by PTSD," Assemblyman Vincent Mazzeo (D-Atlantic). "The VA has stated that it wants each veteran to find the medication with the least amount of side effects that allows them the optimum level of independence. For many, medical marijuana is the drug that best fits that criteria and the only one to provide veterans with significant relief from the anxiety associated with PTSD."

State law recognizes six diseases that qualify patients for medical marijuana if their doctors recommend it: amyotrophic lateral sclerosis or Lou Gehrig's disease; multiple sclerosis; terminal cancer; muscular dystrophy; inflammatory bowel disease, including Crohn's disease; and any terminal illness with a prognosis less than a year.

People with seizure disorders, including epilepsy, intractable skeletal muscular spasticity and glaucoma also qualify if conventional medicine has failed. People with HIV and AIDS and cancer qualify, too, if they suffer from severe and chronic pain, vomiting and nausea and wasting syndrome.

Ken Wolski, a nurse and the executive director of the Coalition for Medical Marijuana of New Jersey, expressed his gratitude to the governor and lawmakers who listened to the veterans' pleas for help.

"As many veterans testified during the hearings in Trenton, marijuana can help control the destructive symptoms of PTSD better than any drug," Wolski said.

The Joint Blog, which bills itself as a "cannabis news and information website," created an online petition last month to push Christie to sign the legislation advocates say will help New Jersey's veterans.

Susan K. Livio may be reached at slivio@njadvancemedia.com. Follow her on Twitter @SusanKLivio. Find NJ.com Politics on Facebook.