"There are clear differences in brain activity between patients who have compulsive sexual behavior and healthy volunteers. These differences mirror those of drug addicts," study author Dr. Valerie Voon, of the University of Cambridge in England, said in a university news release.
Voon's research involved 19 men with sex addiction and a "control group" of 19 men without the disorder, also known as compulsive sexual behavior. The men with sex addiction had started watching pornography, and more of it, at an earlier age than those in the control group.
"The patients in our trial were all people who had substantial difficulties controlling their sexual behavior and this was having significant consequences for them, affecting their lives and relationships," Voon explained.
"In many ways, they show similarities in their behavior to patients with drug addictions," she said. "We wanted to see if these similarities were reflected in brain activity, too."
The study participants' brain activity was monitored while they watched either pornographic videos or sports videos. While watching the pornographic videos, the men with sex addiction showed much greater activity in three areas of the brain compared with men in the control group.
These three areas of the brain -- the ventral striatum, dorsal anterior cingulate and amygdala -- are involved in processing reward and motivation, and also become highly activated in drug addicts in response to drugs.
The study was published July 11 in the journal PLoS One.
"Whilst these findings are interesting, it's important to note, however, that they could not be used to diagnose the condition," Voon cautioned. "Nor does our research necessarily provide evidence that these individuals are addicted to porn -- or that porn is inherently addictive. Much more research is required to understand this relationship between compulsive sexual behavior and drug addiction."
According to the researchers, prior studies have suggested that sex addiction -- an obsession with sexual thoughts, feelings or behavior that they are unable to control -- affects as many as one in 25 adults.
There's more on sex addiction at the U.S. National Institutes of Health.