Combat veterans cannot always leave behind what they saw and experienced on the battlefield when they return to the civilian world. While some ease back into their old lives with minimal problems, many suffer from post traumatic stress disorder so severe that they need professional help to overcome both it and the depression that often accompanies it.

For some, that means seeking relief from their condition through one of the many ketamine centers that have opened in recent years throughout the U.S., where doctors administer ketamine infusions to treat such conditions as PTSD, depression, anxiety, obsessive compulsive disorder, and chronic pain. Extremely good effect is found at stopping suicidal thoughts.

"Some researchers have called the drug the most-important discovery in half a century," says Aimee Cabo Nikolov, administrator of the Ketamine Medical Clinic, Miami, Fla., where about 35% of patients are military veterans seeking treatment for PTSD.

It only is fairly recently that ketamine became popular as a drug for battling such troubling mental-health conditions as PTSD and depression. Originally, ketamine was developed as an anesthetic in the early 1960s, but it was not long before people began using it as a recreational drug that was known on the streets as Special K.

It still is used as an anesthetic but, over time, some in the medical profession began to realize it could be used to treat depression and PTSD. Studies have shown that ketamine infusion can produce significant and rapid reduction in the severity of PTSD symptoms.

Just what is PTSD? Here is what the Department of Veterans Affairs says:

Cause and symptoms. PTSD is a mental health problem that some people develop after going through some sort of trauma, such as experiencing or witnessing a life-threatening event like combat, a natural disaster, a car accident, or sexual assault. Some symptoms include reliving the event, avoiding situations that remind you of the event, having more negative feelings and beliefs, and feeling jittery or always on the alert.

Trauma's effects. Trauma actually is fairly common and does not inevitably lead to PTSD. About 60% of men and 50% of women experience at least one trauma in their lives. For women, trauma is more likely to be the result of sexual assault and child sexual abuse. For men, it is more likely to be because of accidents, physical assault, combat, or a disaster.

Prevalence. About eight percent of people have PTSD at some point in their lives, and about 8,000,000 adults in the U.S. have PTSD in any given year. Women (10%) are more likely than men (four percent) to experience PTSD.