Disregard Everything I Say

Onset : 30-180 seconds
Duration : 5-30 minutes
Normal After Effects : 30-60 minutes
(smoked)

Onset : 10-20 minutes
Duration : 30-90 minutes
Normal After Effects : 30-120 minutes
(sublingual) 

Salvinorum A is a dissociative exhibiting atypically psychedelic effects. It is unique in the fact that it is the most potent natural hallucinogen and the only diterpenoid hallucinogen. The molecule is structurally distinct from other naturally occurring hallucinogens (such as DMT, psilocybin, and mescaline) because it contains no nitrogen atoms. Hence it is not an alkaloid but a terpenoid.  
The only natural source of salvinorum A is Salvia divinorum, a Mexican plant which has a long history of use as an entheogen by indigenous Mazatec shamans but was first described and named by Alfredo Ortega and colleagues in 1982.
The reason it is so unique in terms of its subjective effects is because it has no action at the 5-HT2A serotonin receptor, which is the principal molecular target responsible for the actions of ‘classical’ psychedelics such as LSD and mescaline. Salvia is instead a kappa opioid receptor agonist with a method of action tied into interrupting Kappa-opioid tactile sensory pathways; these pathways mediate pain, gravity awareness, and feedback for determining physical orientation in space. Which explains a few of the subjective experiences found on salvia, which I will describe in detail to you now. 

Bodyhigh:
The physical sensation of a salvia trip is almost entirely characterized by what I call “Salvia Gravity”. This is at least partially present during the mildest of trips and increases proportionally with dosage until it is all encompassing, beginning with a heavy sensation that pulls and tugs at the body. 

As this increases it inevitably becomes so powerful that it swiftly lifts the tripper up and out of their body in a direction that doesn’t make sense. Pushing or pulling them into a space vastly different from anything found on any of the classic hallucinogens.

For some unlucky people this is sometimes accompanied by the sensation of pins and needles all over a persons skin, which for can quickly become very uncomfortable. Most people however will never experience this feeling.

Headspace:
While most drugs usually enhance or heighten certain cognitive functions and simultaneously lower others Salvia does not do this. Instead it lowers everything all across the board and destroys the ego. It’s this effect that contributes to Salvia being extremely confusing, creating for an experience devoid of introspection. Salvia is best described as a substance that does not creates profound insights, just profound experiences.
The average first time user of Salvia generally experiences a mixture of extreme gigglyness and confusion. Paranoia and panic are also very common for the unprepared and this can be accounted for by the fact that k-opoid antaganists have been shown to cause such feelings in people. This can be combated in just the same way that the paranoia induced by weed can be handled. Simply take Salvia in a safe, comfortable environment away from noise and brush off all negative thoughts as irrational paranoia before they can even begin to develop themselves.
A breakthrough Salvia trip feels particularly intense on a mental level with a huge amount of egoloss occurring very suddenly. This feels as if you are receiving the sensory input of your trip, but not fully conscious enough to think about the implications of it until you come down.
Language use is also extremely affected, many users go as far as reporting that their thought processes became replaced with a completely garbled and nonsensical alien language. This is an unusual experience and could be described as pure syntax, completely devoid of meaning.

Visual effects and Hallucinations:
The visual effects of Salvia have a completely alien and unique style to them that is not found anywhere else. Instead of the typical fast flashes of geometric patterns found during a standard psychedelic trip these visuals are of a completely different nature.
Salvia’s typical open eye visuals are unimpressive and rather confusing, a sensation of being flattened into one unified surface is common when a persons eyes are kept open and this seems to play heavily on different sections of your vision. The objects in front of your face also become devoid of meaning.
Closed eye visuals however are most commonly experienced as murky yet defined shapes with a size that is vast and physical in scale. They are not fast moving or transient like your typical closed eye visuals and usually based on mathematical constructs such as elaborate fractals. These constructs are often so huge that they appear to expand for hundreds to thousands of miles and gradually change by means of panning, zooming and rotating slowly into view as more and more detail is gradually revealed. Similar in movement to the structures found on dissociatives such as MXE. 
Entity contact is uncommon but possible. The hallucinations are limitless in their potential and can encompass anything but interestingly enough, the sensation of becoming a random inanimate object is perhaps the most universal. This object could be literally anything but the most common seem to be, conveyor belts, a brick in a wall or a book. The sensation of folding between frames and panels is also quite common.
The hallucinations at low doses, are very murky to look at but still extremely detailed as most of the details are felt instead of seen. For example you may be hallucinating during a breakthrough trip that there is a crowd standing in front of you but although you can barely make them out using your sight you can sense and feel every last one of them in a level of detail comparable to normal vision.

Conclusion:
Salvia is perhaps one of the most confusing experiences a human being can possibly go through. Making it by far the most difficult of all substances which I have attempted to explain.

Some statistics:
A survey performed 6 months ago involving 170 people performed on the r/psychonaut board over at reddit provided this guide with some very useful charts and statistics on the topic of what your average person experiences during a Salvia trip and can be found right here.