shulgin rating scale


Experienced psychonauts are aware of the fact that the psychedelic space can sometimes be tricky to navigate, and know that it is helpful to have techniques available to assist with that effort. Accurately identifying the intensity of an experience can help while the experience is still unfolding, and also once it has concluded and one is attempting to describe the ineffable to others.

Over the course of many years of experimentation with psychedelics, the well-known psychedelic chemist Alexander “Sasha” Shulgin developed a method that can be used to evaluate the perceived strength or intensity of a psychedelic experience. This method has since been named the Shulgin Rating Scale and was published in the introduction to his book PiHKAL: A Chemical Love Story (“PiHKAL” stands for “Phenethylamines I Have Known and Loved.”)

This rating scale only refers to the strength or intensity of an experience, not the content, which can be assessed in other ways. There are a total of five levels of effect, characterized by pluses and minuses, and one additional level that stands alone and is not comparable to the others. Although this scale was originally designed to work specifically with psychedelic substances, it can also be used with substances producing other types of effects, such as stimulants or depressants.


(-) or Minus

At this first level, there are no noticeable effects at all. A person who is at this level is said to be at “baseline” consciousness, which is their normal state. So if the effect of a substance is said to be a minus, then the person would have remained in the same exact state of body and mind they were in prior to its ingestion.


(±) or Plus-Minus

This is the first level at which the substance causes the person’s consciousness to shift away from “baseline.” However, at the plus-minus level the user cannot be completely sure that the change in consciousness is a direct result of having taken the substance. Because of this, there can be a lot of false positives in this category. Signs of activity may often prove to result from the person’s imagination as opposed to actual effect.

Shulgin notes in PiHKAL that it can be useful to develop what he termed an “alert”: a small sign, occurring early on in an experiment, which reminds the person that they have taken a psychoactive substance and may be beginning to experiencing its effects. Each person would identify their own unique alert after many psychedelic experiences. Examples of alerts could include things like a tingling sensation in the back of one’s head, a particular feeling in the throat, or a slight difference in visual acuity.


(+) or Plus-One

When an experience has crossed over into plus-one territory, it is now obvious that there is a real effect being experienced. It will be possible to determine the duration of that effect, but not its character. Many times, this initial effect will be physical in nature, such as the onset of nausea, lightheadedness, or compulsive yawning. These early physical effects tend to go away within the first hour (if they are experienced at all), but they should be considered real, not imaginary. If any mental effects are noticed, the person will not be able to identify their qualitative nature. It is rare for there to be false positives at the plus-one level.


(++) or Plus-Two

Once an experience has reached the plus-two level, the substance’s effect has become unmistakable and both its duration and nature can be perceived. However, an experienced psychonaut will have some choice as to whether he or she will accept the adventure, or continue with the ordinary day’s plans instead. In other words, the substance’s effects can be allowed to have a predominant role, or they can be repressed and made secondary to other activities.


(+++) or Plus-Three

The fifth level, plus-three, describes the maximum intensity of a substance’s effect that can be experienced. Both the duration and nature of the substance’s action become extremely clear. The entire chronology of the substance’s effects can be determined, from the exact time that the alert makes its appearance, to how long the full activity of the effect occurs, to the first sign that the decline to baseline is about to commence, and finally how steep or gentle that decline to baseline will be. In addition, ignoring or repressing the effects of the substance is no longer possible, rendering the experimenter completely engaged in the experience, for better or worse.


(++++) or Plus-Four

The sixth (and final) level is a separate and special category that Shulgin placed in a class of its own, independent from the levels of intensity previously discussed. A plus-four effect is not meant to imply that it is more than, or comparable to, a plus-three. This is a rare transcendental state, which could be described as a “peak experience” or “divine transformation” that is not necessarily dependent on which substance has been consumed. It can be characterized as a state of bliss or a feeling of universal connectedness, and cannot be repeated at will by repeating the ingestion of that particular substance. These are the types of unique (and often life-changing) experiences that are described as mystical or even religious, which are never forgotten and often bring a lasting change of perspective to the person who experiences them.




Although it can be challenging to assess the intensity of a psychedelic experience, the Shulgin Rating Scale is one way to analyze the duration and nature of a substance’s effects. Reflecting on past experiences with this method in mind can help you learn about what you went through, and this scale can also be used to find common ground when describing your experiences to others.