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Philippine President Ferdinand Marcos on Monday brushed off accusations by Rodrigo Duterte that he was a "drug addict", saying his predecessor's long-term use of fentanyl had taken a toll on his health.
Marcos's comments came after Duterte launched a foul-mouthed tirade against his successor over a campaign to change the country's constitution, in the latest sign of a breakdown in relations between the powerful families.
Fronting a rally of supporters in his southern stronghold of Davao city on Sunday, Duterte said Marcos was a "drug addict" and had been included in the Philippine Drug Enforcement Agency's (PDEA) list of people linked to illegal drugs.
Duterte provided no evidence for the accusations and the PDEA issued a statement on Monday saying Marcos "is not and was never in its watch list".
"I think it's the fentanyl," Marcos told reporters when asked about Duterte's allegations.
"It's highly addictive, and it has very serious side effects. PRRD (President Rodrigo Roa Duterte) has been taking the drug for a very long time now," Marcos said.
Fentanyl is a synthetic opioid many times more powerful than heroin.
Duterte, whose bloody crackdown on narcotics left thousands of people dead and sparked an international investigation, has previously admitted using fentanyl for pain relief.
The two families formed a formidable alliance ahead of the 2022 elections, with Marcos successfully running for president and Duterte's daughter, Sara Duterte, for vice president.
Since then, however, their so-called "Unity Team" has fractured as they seek to shore up their respective support bases and secure key positions ahead of next year's mid-term elections and the 2028 presidential race.
Sara Duterte and Marcos's cousin and House of Representatives Speaker Martin Romualdez are widely expected to run for president.
In the latest rift, Marcos has backed a campaign for the 1987 constitution, introduced after his dictator father and namesake was ousted from power, to be changed to allow in more foreign investment -- something the Dutertes have publicly opposed.
Critics warn the effort could pave the way for Marcos to seek another six-year term, which is currently prohibited.
That would potentially put him on a collision course with Sara Duterte for the top job.
Sara Duterte said Monday that her brother Sebastian's suggestion on Sunday that Marcos resign came from "a place of brotherly love" and alleged she was being subject to "despicable treatment" by "some sectors within the circle of the President".
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