Ashton Kutcher took medication in a bid to prevent going bald. (Pic: Evan Agostini /AP)

Ashton Kutcher began treatment to stop himself going bald at the age of 25, but quit five years ago and is now embracing his thinning locks.

The 40-year-old actor - who has two children, Wyatt, three, and Dimitri, 14 months, with wife Mila Kunis - started worrying about losing his hair when he was just 25 years old, but quit the treatment five years ago and has now accepted his receding hairline.

Mila Kunis and Ashton Kutcher with their kids. (Tibor Illyes/MTI via AP)

He admitted: "I've gone off of anything to retain my hair. I started getting very concerned when I was 25, and that's when I went on the Avodart. And I think like, five years ago I stopped and I did really good for a year, and now it's thinning out."

And the former 'That 70s Show' star insisted he is "comfortable" with losing his locks now he is a married father.

Speaking to pal Dax Shepard on his new podcast 'Armchair Expert', he added: "I've actually become comfortable with it. I'm just good with it. I've got kids now."

And Dax - who has Lincoln, four, and Delta, three, with wife Kristen Bell - admitted he had also sought treatment to preserve his locks.

He said: "I had heard that there was this doctor that would give you hair as thick as Brad Pitt's, and I was going to this guy and I was doing it for two years and I was like, 'What am I doing?' I think we both went to this doctor."

Meanwhile, Ashton - who was previously married to Demi Moore - admitted he has never been a big drug user but did experiment with various illicit substances when he was in high school.

He said: "When I was in high school and college, I smoked weed some and did mushrooms and tried acid and did some various things that were expansive for me at the time.

"So, I did a ton of that fun stuff when I was younger. And then when I went to college, I was like, 'I'm done.' I think that I smoked weed like one time when I was in college, and then after I dropped out and moved to Los Angeles.

"And so I didn't do drugs. I had entered into a pretty long run of sobriety from drugs, and I didn't really drink that much. If we went out during the weekends, I would drink, but I always kind of had a school night rule. 

"If I had work the next day, I wasn't really going to. And I bent it a couple times here and there, but for the most part I really had a relatively sober living."