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Side Effects of Hallucinogens

As a group, hallucinogens are best known for their ability to alter sensory perceptions and create altered states of consciousness. According to the National Institute on Drug Abuse, hallucinogens work by altering serotonin levels in the brain. Serotonin, a primary neurotransmitter chemical, regulates:

  • Mood states
  • Arousal
  • Cognition
  • Stress responses

In effect, a hallucinogen “high” resembles a psychotic state where users lose their grasp on reality and enter into a world of their own making. Side effects of hallucinogens develop out of the chemical changes that take place in the brain.

Types of Hallucinogens

Hallucinogens can be broken up into three primary groups, each of which produces its own range of effects:

  • Dissociatives
  • Deliriants
  • Psychedelics

Not surprisingly, side effects of hallucinogens can vary depending on the category of drug used. While all hallucinogens act on a person’s sensory perceptions, different types of hallucinogens alter sensory perceptions in different ways.

Dissociative drugs essentially prevent the brain from processing incoming sensory stimuli. In response, the brain creates its own internal reality and perceptions. Deliriant drugs create false perceptions that leave users in a confused, stupor-like state. Psychedelics expand a person’s sensory field allowing the brain to process intricate and/or enhanced details from a person’s surrounding environment.

Considering how hallucinogens target the brain’s sensory processing centers, many side effects of hallucinogens directly impact a person’s cognitive abilities.

Side Effects of Hallucinogens

Unlike opiates and stimulants, hallucinogens induce a complex series of chemical events within the brain via its effects on serotonin output. According to Bryn Mawr College, depending on the type of drug, side effects of hallucinogens may result from changes in other neurotransmitter levels brought on by the influx of serotonin.

Both dopamine and norepinephrine can respond to fluctuations in serotonin. Dopamine plays a central role in regulating pain/pleasure sensations, whereas norepinephrine has more to do with arousal states and the body’s stress response. In turn, side effects of hallucinogens can stem from norepinephrine’s arousal-based functions or dopamine’s pain/pleasure-based functions.

Increasing Tolerance Levels

Regular or frequent hallucinogen use taxes brain cell secretion processes to the point where cell structures start to weaken. After a certain point, hallucinogen effects decrease in intensity as cells lose their ability to produce serotonin.

This side effect of hallucinogens increases the brain’s tolerance for the drug so users have to keep increasing dosage amounts over time. The shorter the duration between doses the faster tolerance levels rise.

Along with increasing tolerance levels, another related side effect of hallucinogens takes the form of cross-tolerance with other hallucinogen drugs. This means the brain develops a tolerance for all drugs in this class as opposed to just one type of hallucinogen.

Short-Term Effects

Short-term side effects of hallucinogens can vary based on the type of hallucinogen used. While sensory-based effects predominate, users can also experience a range of physical effects as well.

effect of hallucinogens

One effect of hallucinogens is seeing bright colors and light trails.

Sensory side effects of hallucinogens include:

  • Distorted sense of time
  • A merging of sensory perceptions, such as hearing colors and smelling sounds
  • Seeing bright colors
  • Seeing tracers or light trails
  • Seeing imagined imagery

Physical side effects of hallucinogens include:

  • Elevated blood pressure rates
  • Elevated heart rates
  • Increased breathing rates
  • Fine tremors
  • Extreme changes in body temperature, alternating between chills and hot flashes
  • Seizure potential
  • Muscle stiffness

“Bad Trips”

As one of the side effects of hallucinogens, the inherent risk of experiencing a “bad trip” doesn’t exist for other types of addictive drugs. According to the U. S. Drug Enforcement Administration, at any given time, users may experience a “good trip” or a “bad trip” depending on a range of factors, including:

  • Mood state during time of use
  • Surrounding environment
  • Expectations of the drug

While “good trips” can bring on exhilarating experiences that border on the divine or spiritual, “bad trips” come with frightening, unsettling sensory-based experiences. This side effect of hallucinogens can produce:

  • Seeing disturbing images
  • Feelings of extreme anxiety or terror
  • Feelings of deep, dark despair
  • The sensation of bugs crawling along the skin


Addiction, in general, develops once a person becomes psychologically dependent on a drug’s effects. Psychological dependency makes a person feels as if he or she can’t cope with daily life without the effects of the drug.

This side effect of hallucinogens only develops in cases of frequent, ongoing drug use. In effect, brain chemical imbalances caused by the drug’s effects have warped the brain’s reward system, the region that determines a person’s priorities, motivations and overall belief systems.

As a side effect of hallucinogens, signs of addiction typically take the form of:

  • Neglecting work responsibilities
  • Relationship conflicts brought on by drug use
  • Money problems
  • Problems with the law, such as driving under the influence or engaging in criminal activity


As hallucinogen “highs” normally take the form of a drug-induced psychotic state, people who use on a regular, long-term basis stand the risk of developing a full-blown psychosis, according to Psychology Today. This side effect of hallucinogens can persist for years after a person stops using drugs, essentially destroying his or her overall functional capacity.

Psychosis-based side effects of hallucinogens include:

  • Loss of touch with reality
  • Extreme mood swings
  • Profound depression states
  • Inability to communicate with others in a coherent fashion
  • Disorganized thinking processes

Hallucinogen Persisting Perception Disorder

For some people, the hallucinations experienced when using leave a lasting imprint on the brain’s ability to process sensory information. This is especially the case for former LSD users. This side effect of hallucinogens, known as Hallucinogen Persisting Perception Disorder or HPPD produces flashback episodes of previous drug “highs,” which can occur at any given time. Like psychosis, this condition can continue for years after a person stops using.


Compared to other types of drugs, hallucinogens carry a low abuse/addiction potential overall; however, the side effects of hallucinogens do pose certain dangerous for long-time users. Ultimately, the effects of these drugs on brain chemistry can bring on serious repercussions, especially for people with a history of psychological problems.

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