ALTERED STATES

In 1967, Edward Jessup is a Columbia University psychopathologist studying schizophrenia. He thinks that "our other states of consciousness are as real as our waking states." He begins experimenting with sensory deprivation using a flotation tank, aided by like-minded researchers, Arthur Rosenberg and Mason Parrish. At a faculty party, he meets fellow "whiz kid" and his future wife, Emily.

Over a decade later, Edward is a tenured professor at Harvard Medical School. He and Emily have two daughters and are on the brink of divorce when they reunite – for the first time in seven years – with the couple who had first introduced them. When Edward hears about the Hinchi tribe, whose members experience shared hallucinatory states, he decides to travel to Mexico in order to participate in their ceremony.

During the climb up into the Hinchi hill country (a plateau covered in spectacular mushroom-shaped ventifacts), Edward is told by his guide, Eduardo Echeverria, that the Hinchi use in their ceremonies a potion containing the sacred mushroom Amanita muscaria and the shrub sinicuiche, which they are collecting for next year's ceremonies. The tribe calls sinicuiche by a Hinchi name meaning "first/primordial flower" in recognition of the deep memory states which it can evoke. An indigenous elder ("the brujo") is seen with a root in his hand, which he asks Edward to hold, before cutting Edward's hand in order to add drops of blood to the mixture he is preparing. Immediately after consuming the mixture, Edward experiences bizarre, intense hallucinations, including one of the petrifaction and subsequent erosion by blown sand of Emily and himself.

The following morning, Edward leaves the Hinchi plateau under a cloud, having killed, while in his intoxicated state, a large specimen of the Hinchi's sacred monitor lizard. He returns to the U.S. with a sample of the Hinchi potion for analysis by his colleagues and further self-experimentation and continues taking it in order to take his exploration of altered states of consciousness to a higher level.

When toxic concentrations of the substance make increased dosage dangerous, Edward returns to sensory deprivation, believing it will enhance the effects of the substance at his current dose. Repairing a disused tank, he uses it to experience a series of increasingly drastic visions, including one of early Hominidae. Monitored by his colleagues, Edward insists that his visions have "externalized". Emerging from the tank, his mouth bloody, frantically writing notes because he is unable to speak, he insists on being X-rayed before he "reconstitutes." A radiologist inspecting the X-rays says they belong to a gorilla.

In later experiments, Edward experiences actual, physical biological devolution. At one stage, he emerges from the isolation tank as a feral and curiously small-statured, light-skinned caveman, going on a rampage in town and breaking into a zoo before returning to his natural form. In the final experiment, he experiences a more profound regression, transforming into an amorphous mass of conscious, primordial matter. An energy wave released from the experiment stuns Edward's colleagues and destroys his tank. Emily recovers and finds a swirling maelstrom where the tank had been. She searches in the vortex for Edward, finding him as he is on the brink of becoming a non-corporeal energy being that will vanish from reality if this transformation reaches its conclusion.

His friends bring Edward home, hoping that the transformations will end. Watched over by Emily, Edward begins to regress uncontrollably, the transformations no longer requiring the intake of "first flower" or sensory deprivation. Urging Edward to fight the change, Emily grabs his hand, being enveloped by the primordial energy emanating from him. The sight of Emily apparently being consumed by the energy stirs the human consciousness in Edward's devolving form. He fights the transformation off by banging repeatedly into the hallway wall and returns to his human form. Edward then grabs Emily's form, and she returns to normal. The movie ends with the two on the floor in a nude embrace as Edward tells Emily that he loves her, which she had longed to hear him say.

In the film’s climax, Jessup’s relentless experiments culminate in a final transformation that threatens to consume both himself and reality, but his connection with Emily ultimately halts the process, restoring his humanity.

The ending underscores the risks of unchecked scientific obsession and the fragility of identity when reality itself is mutable. Jessup’s ordeal suggests that love and human connection can serve as the anchor to reality, even when consciousness itself is on the brink of dissolution. The film resolves its cosmic questions with an intimate, emotional answer—anchoring metaphysical terror in the power of human relationships.