The following experience was reported on the internet. This person smoked a single hit of dried Salvia divinorum leaf through a water pipe.  He estimates the amount of material at under 1.2 gram, and it was not potentiated by any other substance.

Upon inhaling and holding a large hit:
 

"After about 15 seconds I realized I could hold my breath as long as I wanted. My cells seemed to still be respirating somehow, and I thought that breathing is really a luxury, something we do more out of habit than anything else. This alarmed me, and I exhaled. While I exhaled, I received a flood of colorful visions, swirling patterns of light against a dark, outer space-like background. This swirl formed into a tunnel, which led from somewhere in front of me (maybe 20 yards in front of my center of vision) to "behind" my eyes. By thinking about it, I could move my perspective a little bit. My peripheral vision and imagination was filled with what seemed like two beings. One was old and male, one was young and female. They were encouraging me to look straight through the tube, aligning my center of vision with it. Well. this tube thing was very soft and flexible. and any attempt to look through the end caused it to wrinkle somewhere in the middle, ruining my straight view through it. After some practice, I was able to get a brief glimpse into a fractal dimension of untold complexity. Around the "mouth" of this tube were several other tubes, each with the same view inside. I was presented with the fact that these tubes were the building blocks of cellular matter, and the word "nucleotide" was loud in my head. I don't even know what it really means, but the voice was telling me it was what I was looking at. They were saying "a little to the right, come on, don't wait until you're dead to see this, it's great !" The whole thing, while fascinating, had a bit of a nausea-like flavor due to a physical/mental "turbulence", like my mind was doing somersaults."

"After giving up my effort to hold the tube straight enough to see through, I remembered that I existed, and realized I was coming down, The mouth of the tube drew away from me, or I fell away from it was like coming out of a black hole, and then being able to observe the mouth suddenly...This tube can be visualized somewhat by imagining a funnel. It felt like a diagram I've seen of a black hole. An index card is covered with a grid. The center of the grid is pulled into another plane, and the result is a funnel shape. This funnel connects the black area behind the eyes to a distant coordinate in time/space... The tube was formed by reality itself (meaning what I usually take for ërealityí) curving in upon itself."