Two questions.

I read somewhere that salvia triggers the Opioid receptors in the brain. Is this true?

Also, if the first is true, if you were to take some morphine and let it kick in before smoking the salvia would it make the experience any better?

it does not "trigger" THE opioid receptors in the brain. it agonizes kappa-opioid receptors in the brain, completely different from the mu-opioid receptor which opiates bind to.

if you were to take morphine then smoke salvia, it would obviously make the experience more enjoyable, but morphine makes every experience more enjoyable. they are not related in any way, and the fact that you would be high on morphine is the only reason it would make the experience more enjoyable, although it would probably dull the effects of salvia.

Well, Salvia works on the Kappa opiate receptor. That receptor is responsible for the dreamy, hallucinogen like effects that sometimes accompany opiate use. Painkillers like morphine mainly work on the delta and mu receptors.

My guess is that if you took morphine before taking salvia you might just block the effects of the salvia all together or diminish them quite a bit. Once opiate receptors are occupied, a much stronger drug is needed to "knock" the drug off and replace it.

I would check erowid experiences for combinations like that

Edit--- I've also heard that people on methadone or buprenorphine maintenance have a harder time getting off on salvia.