Schoolkids today are watching porn like never before. It's free, it's instant and it's having a devastating effect.

3D has spoken to porn users and porn addicts, as well as a sex educator and a top international scientist who say this new type of porn can actually alter our brains.

The vast majority of teenage boys are into it, as well as a surprising number of girls. If it were cocaine and children we were talking about, we'd be shouting about it from the rooftops. But porn is embarrassing and no one wants to talk about it.

Research suggests the average age New Zealand children are exposed to internet porn is 10. Looking at pornography can become a daily habit for users, and what they see on the screen is what they want in the bedroom.

For 19-year-old Adam [not his real name] the past few years have been a wipe-out.

"I was just completely unmotivated for anything, depressed, barely could find a reason to get up in the morning," he says.

"I basically didn't care what I was doing in school at the time. I didn't care if I was failing or succeeding. The teachers were worried, but they eventually, I think, kind of gave up on me."

Adam started watching internet porn when he was 12.

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"At least four times a week, sometimes up to twice a day, or even more."

It wasn't until last year that Adam realised what was happening to him, when he tried to stop.

"It took me, probably, six months of continuous trying until I made it to about two weeks without it."

But how could he get help? Even if he could get up the guts to talk about it, porn addiction isn't an accepted medical condition. Adam had to turn back to the internet.

On a site called Reboot Nation, Adam found thousands of young men in the same boat. Gabe Deem is the founder of Reboot Nation and another young man who doesn't fit the stereotype of the loser living in his mum's basement.

"There are tonnes of guys that grew up on internet porn that just watch porn because we liked it," he says. "We like watching naked girls have sex. And then we develop problems after years of conditioning ourselves to that. So we don't have social problems, we don't have relationship problems to start with. Those develop after porn use and it's happening to everyone who has unlimited access to porn."

Mr Deem started viewing cable porn regularly when he was eight. Four years later his parents got high-speed internet.

"I had no idea that it could have a negative physiological impact on me, no clue. At the time it was all jokes, giggles and pleasure. Never really thought how it was impacting me, never really cared how it was impacting me. I didn't realise it was a problem until I had porn-induced erectile dysfunction when I was 23, when I realised I could no longer be aroused with the real partner and I became dependent on porn to feel anything."

Mr Deem started having trouble getting aroused with his partner; he could only get an erection behind a computer. All the porn he had been watching had done something to his brain.

Porn on the brain

Don Hilton has been peering inside people's heads for 21 years. A brain surgeon in San Antonio, he is a world expert.

"I think there's ample evidence that pornography rewires the brain in a very dramatic fashion," he says.

Four years ago Dr Hilton put forward the controversial theory that internet porn could be as addictive as cocaine.

"We predicted that based on the way sex causes these reward chemicals in the brain to be produced, that we would see some of the brain scan findings that we find with drugs."

The latest research is proving him right. At Cambridge University they scanned the brains of 19 compulsive porn users and 19 other men while watching explicit porn. Researchers wanted to know what would happen to their reward centres. That's the part of the brain that lights up when we do things we enjoy, like eating or having sex. It's fuelled by packets of dopamine.

While the control group got a little buzz from the porn, the reward centres of the porn users lit up like Christmas trees, just like the scans of cocaine addicts. They wanted more and they wanted it now.

Critics say there's no such thing as porn addiction, that it's just people with high libidos doing their thing.

But last year there was more supporting evidence. The Max Planck Institute in Germany identified two physical changes in the brains of internet porn users. First, there was a rewiring of the frontal lobe, the part of the brain that exercises willpower – our braking system.

"It's essentially wearing out the braking system," says Dr Hilton. "It's impeding the signal from the brake to the reward centre. So the brake doesn't work as well."

The second and most stunning neurological discovery is that high-speed internet porn might actually shrink the brain.

"This shrinkage in the reward area was pronounced the more hours per week the person watched pornography.

That means less grey matter in the part of the brain associated with decision-making and motivation. It makes sense of Adam's symptoms.

There's a third aspect of this emerging science that is even more worrying from a social point-of-view. The more porn you watch, the more extreme your brain wants it to be.

But why would our brains do that to us?

"Novelty," says Dr Hilton. "Now our brains want to learn something new. We're always trying to learn something new. It's what we do. Our brains want to learn and we need new, and new is aggression, new is younger."