President Rodrigo Duterte said he is taking marijuana to keep him awake but he later clarified it in an ambush interview with reporters after speaking at a Malacanang event.

Duterte, who declared war on illegal drugs, made the admission during the conferment awards on ASEAN National Organizing Council Officials and Personnel on Monday.

He made the revelation while recalling his busy schedule when he was in one of the ASEAN events abroad.

"It's a killing activity, and I think at my age, I could hardly (sleep) because I'm taking marijuana to keep me awake. Others could not keep up," Duterte said, noting there was an instance that he saw Brunei Sultan Hassanal Bolkiah who was sleeping in one of the leaders' meetings.

After that event, Duterte said he was joking. "I want to shake a tree in the middle of a... You know, I was just cracking a joke. (It's) boring if there is no (joke)."

"Do you really believe me, using marijuana?," added Duterte.

Presidential Spokesperson Salvador Panelo said people should be used to Duterte's style. "Every now and then he cracks jokes during a speech," said Panelo.

In several press interviews, Duterte said he was in favor of legalizing medical marijuana.

There is a pending bill in Congress to legalize medical marijuana, but it has not prospered yet due to opposition by some quarters. Celerina Monte/DMS