President Marcos suspects that former president Rodrigo Duterte's claim that he was into illegal drugs may have been brought about by the fentanyl that his predecessor has reportedly been taking.

Marcos said this a day after Duterte alleged that Marcos was into illegal drugs, and was even included in the watchlist of the Philippine Drug Enforcement Agency (PDEA).

The PDEA has denied ever having Marcos in any of its watchlists.

In an interview, before he flew to Vietnam for his State Visit, the President said fentanyl was a highly addictive substance that could affect anyone who has been taking it for years.

"It is highly addictive, and it has very serious side effects. And PRRD (Duterte) has been taking the drug for a very long time now," Marcos told reporters on Monday, Jan. 29.

"When was the last time he told us that he was taking fentanyl? Mga five, six years ago? Something like that. After five, six years, it has to affect [him]. Kaya palagay ko kaya nagkakaganyan (That's why I think he's acting this way)," he added.

Marcos expressed hope that Duterte's doctors are taking good care of him.

"I hope his doctors take better care of them, hindi pinapabayaan itong mga nagiging problema (They're not letting it become a problem)," he said.

In December 2016, former president Duterte admitted that he took more than the required dosage of fentanyl to ease the pain he sustained after a motorcycle accident when he was 68 years old. He said the fentanyl made him feel like he was "on cloud nine."

The Centers for Disease Control and Prevention (CDC) describes pharmaceutical fentanyl as a synthetic opioid used to treat severe pain. It is said to be at least 50 times more potent than morphine.

Meanwhile, when asked to categorically deny that he was into illegal drugs to put the issue to rest, President Marcos just let out a laugh.

"I won't even dignify the question," he said.

This was not the first time that former president Duterte dropped hints about his successor and drug use. In November 2021, Duterte hinted that the leading presidential candidate was into cocaine.

Days before Duterte's allegations in 2021, Marcos actually tested negative for shabu. In November 2022, he had himself tested for cocaine, which eventually came back negative.

The PDEA also denied on Monday that Marcos was never on its drug watchlist.