In his controversial memoir Spare, Harry admits to regular drug-taking and describes how in 2015, while living in Nottingham Cottage in the grounds of Kensington Palace, he smoked marijuana.
On Saturday, he spoke to Dr Gabor Mate, author of The Myth of Normal: Trauma, Illness and Healing in a Toxic Culture, in a livestreamed interview, with topics including his use of cocaine, marijuana and alcohol.
"(Cocaine) didn't do anything for me, it was more a social thing and gave me a sense of belonging for sure, I think it probably also made me feel different to the way I was feeling, which was kind of the point," Harry said.
"Marijuana is different, that actually really did help me."
The duke also told of using psychedelics such as ayahuasca.
"It was the cleaning of the windscreen, cleaning of the windshield, the removal of life's filters just as much as on Instagram, these layers of filters," Harry said.
"It removed it all for me and brought me a sense of relaxation, release, comfort, a lightness that I managed to hold on to for a period of time.
"I started doing it recreationally and then started to realise how good it was for me, I would say it is one of the fundamental parts of my life that changed me and helped me deal with the traumas and pains of the past."
Harry also spoke about the death of his mother, Diana, Princess of Wales, who died in a car crash in Paris in 1997 when the duke was just 12 years old.
Mate told him: "Reading the book, I diagnose you with ADD....I see it as a normal response to normal stress."
He said this could be "healed at any age".
Harry's ghostwritten tell-all autobiography laid bare his frustrations with his family.
He claimed his brother William, now the Prince of Wales, had knocked him to the floor at Harry's then home Nottingham Cottage after calling the Duchess of Sussex "difficult", "rude" and "abrasive".
The duke claimed his father, now King, put his own interests above Harry's and was jealous of Meghan and Kate, and that the Queen Consort sacrificed him on "her personal PR altar".
The duke, who lives in California after moving to the US in 2020, has revealed he has enough material for two books but held back because he does not think his father and brother would "ever forgive" him.
It has not yet been confirmed whether Harry will be invited to attend his father's coronation in May.
AAP with The Project.