Well to be fair it seems unlikely that they would get a salvia trip off that anyway since you have to hold it in, and it would be an unpleasant 5 minutes or so if it did, but I still think drugging people without their knowledge unless it's something you know they would want is wrong.
When I say know they would want I mean like, once I was camping with my hippie type friends and I gave them caramels laced with weed without mentioning it, and they were happy when they realized it. I knew they would be happy about it otherwise I wouldn't have done it.