Opium makes you sluggish, which makes difficult to carry out the kind of attacks that juramentados made, the kind of attacks they were known to make for centuries before the traders brought them opium.
Opium increases pain tolerance which was its purpose when used by the Moros.
Furthermore Opium was imported into what would become the Philippines in the mid-Sixteenth Century. Chinese were emigrating to the Philippines in significant numbers and bringing their opium trade with them starting in the 1600's. The Spanish issued a Royal Decree in 1814 forbidding the Opium Trade and Use in the Philippines... then in 1828 decided to cultivate it themselves for the purpose of export.
The Spanish term of Juramentado as a placeholder for Jihad Warrior wasn't coined until centuries after the introduction of Opium, which was chronicled as being in wide use amongst the Moros as well. While there was always conflict with the Moro population in the Southern Philippines, the idea of "Holy War" against Christians/Spanish wasn't really until the Spanish established themselves in Moro held territory of the Sulu Archipelago in the mid-19th Century.
Also as a petty aside, there was more to Moros then Juramentados. Actual Islamic Suicide Warriors were small in number. There were Moro Warriors who engaged in near suicidal attacks, but it was far from ala due to institutionalized Islamic suicide attacks. Like comparing actual suicide bombers to ISIS or the Taliban at large or Kamikaze pilots to the Imperial Japanese military at large the latter of whom might have 'suicidal' courage in battle.
The Juramentados as I define them, undergo the requisite purity rituals that are vaguely similar to the ones that Islamic suicide bombers have undergone with the ablutions and purifications and other rituals including ones involved with imbibing resin incense and the like. AFAIK Opium isn't involved in it, but opium was likely used by Moro warriors before hostilities in a general sense. The Spanish and some American/Filipinos having no distinction between Moros (Juramentado is basically a Spanish term after all) thus is either right or wrong depending on how you interpret the that specific term.
Which is why I was referring to Moro Warriors in general.