Lysergic acid diethylamide (LSD) is a potent synthetic hallucinogen derived from a fungus that grows on grains, most commonly rye. This substance is colorless and odorless, but even a tiny amount can produce powerful psychological effects by acting on serotonin receptors in the brain, particularly the 5-HT₂A receptor. These acute, short-term effects, commonly referred to as a “trip,” range from involuntary physical responses to profound alterations in perception, emotion, and thought processes.
Physical Manifestations
The ingestion of LSD triggers involuntary changes in the body as part of the initial response. Within the first hour, users typically experience changes in vital signs, including an increase in both heart rate and blood pressure. The drug also often causes a rise in body temperature, which can lead to uncomfortable sensations of flushing, chills, or excessive sweating.
One of the most consistently reported physical signs is mydriasis, or the dilation of the pupils. Other physical symptoms can include tremors, weakness, or dizziness. Some individuals may also experience temporary physical discomfort, such as nausea or a dry mouth.
Perceptual and Sensory Alterations
The primary effect of LSD involves an animated sensory experience where the brain processes external stimuli in an altered way. Visual perception is affected, with colors often appearing more vivid and intense than usual. Objects may seem to morph, ripple, or move, and users frequently report seeing geometric patterns, halos, or trails following moving items.
This altered processing involves a shift in brain connectivity, where regions responsible for sensory functions show increased communication. The perception of time is frequently distorted, leading to the sensation that time is speeding up or, more commonly, slowing down. Auditory perception can also be altered, resulting in intensified sounds, echo-like distortions, or a profound experience of music.
A phenomenon known as synesthesia occurs when the boundaries between different senses seem to blur. This crossover can manifest as “hearing” colors or “seeing” sounds, creating a blending of sensory input. The drug’s effect on the serotonin 5-HT₂A receptor is strongly implicated in these shifts in sensory processing.
Cognitive and Emotional Impact
The psychological experience under LSD is highly variable and can involve profound shifts in mood and thought processes. Thought patterns can become philosophical, abstract, or circular, characterized by an accelerated pace. LSD can produce rapid and intense mood swings, where a person may transition quickly between states of euphoria and bliss to severe anxiety or despair.
Altered self-perception is common, which may include feelings of depersonalization or derealization, where the individual feels separated from their body or that their environment is not real. In some cases, the experience can involve a feeling of ego dissolution, where the sense of self temporarily breaks down. While some users report increased emotional empathy, others may experience intense feelings of paranoia, suspicion, or fear of losing control.
The drug can induce a state resembling psychosis, marked by cognitive disorganization and delusional thinking. This effect is distinct from the sensory changes and represents the psychological turmoil that can accompany the experience. The emotional outcome is highly dependent on the user’s mindset and the environment where the drug is taken.
Acute Risks and Duration
The effects of LSD typically begin within 30 to 90 minutes after ingestion, with the most intense phase occurring between two and four hours. The total duration of the short-term effects generally lasts between 6 and 12 hours, though some lingering effects may persist for up to 24 hours. Because of this lengthy duration, the experience cannot be quickly ended once it has begun.
The most significant acute risk is the “bad trip,” characterized by fear, panic attacks, and anxiety. During this negative experience, the temporary psychological distress can sometimes resemble a psychotic episode, involving terrifying thoughts and paranoia. The profound alteration of perception and judgment also creates a physical danger, as the user’s impaired sense of reality can lead to unpredictable behavior and an increased risk of accidental injury.