Jake Paul has revealed boxing has already taken a toll on his brain despite only being four fights into his professional career.

Paul - who fights for the third time this year when he rematches Tyron Woodley on December 18 - said he has started to forget and slur his words since taking up the sport.

The YouTube star underwent a brain scan before devoting his future to the ring, with doctors advising him against competing due to previous concussions he suffered in American football.

And the 24-year-old said damage to his brain had worsened when he underwent a brain scan after his first year in boxing.

"I got my brain scanned right before I started boxing and the doctor told me there's lack of blood flow from the concussions I had playing football to certain areas on my brain," he told Graham Bensinger.

"One of them I believe is the frontal lobe which is partial for memory and so on. After my first year of boxing I went back and it was worse.

"[The doctors] advice is don't do that sport. That's all they can advise as a doctor, I think before it was affecting me at a rapid pace because I never took it easy.

"I was always thrown in there with people who were way better than me until I started to slowly get to their level."

Jake Paul revealed the toll boxing has taken on his brain

Contact sports such as boxing and American football have been linked to brain conditions such as CTE (chronic traumatic encephalopathy) due to the repeated blows athletes take to the head.

As Paul describes, some symptoms of CTE are memory loss, forgetfulness and slurred speech.

The 24-year-old also claims that psychedelic drugs such as DMT that have helped ease the symptoms of his brain damage.

"You're doing something that is detrimental to your long term health," he continued.

"I notice it in conversations with my girlfriends or friends, not remembering something that I should be able to remember that happened a couple days ago.

"Sometimes in my speech, there's like every 100th or 200th word I'll mess up or like slur, which I didn't do that before.

"I've talked to tons and tons of people about it and there's new research and science to combat against it, things like psychedelics and toad."

Former heavyweight champion Mike Tyson - who is an advocate for psychedelics - has claimed to have "died" whilst smoking toad but also credited it for helping him concentrate more.

And Paul continued: "It sounds crazy but it can actually increase the neural activity in your brain and open up new pathways, I've experimented with that and it's definitely helped."