The 59-year-old father of pop star Lily Allen agreed to take part in a TV trial to allow scientists to analyse the effects of the substance on the brain and body.
Participants were given pure MDMA in one session, while in another they were told to take a placebo - and Allen admits he found it hard to tell the difference between his experiences.
Footage of the experiments aired in the U.K. on Thursday night (27Sep12), and the actor admitted during the trial that it was a surreal time.
He says, "I'm interested in it because I dont think I've had proper E (ecstacy) since 1988. Everytime I've taken this stuff it's been in a social environment. I believe that there is no external stimuli, so it's just me and my brain.
"While I was in the tube (scan), I was asked three times about what effect the MDMA was having on me and I said none. As soon as I came out and I looked at the light I went, 'Hang on a minute I've had something here'. But there was no rush, no extraordinary (feelings). I was definitely light on my feet without a shadow of a doubt, I felt I was going to fall over.
"I can feel, it's more a physical thing than a mental thing, unless I'm having a f**king brain haemorrhage or something, coming out and walking down the corridor. I've definitely been given something. If I was in a tent with booze and what have you and music I'd probably be going mental."
Speaking in the studio audience of Drugs Live: The Ecstasy Trial, he added, "I'm really amazed looking at that. I would put my house on the fact that I wasn't on MDMA, I thought I was on something, but not MDMA."