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by E. Jonathan Arnett

Excerpted from:
Psychological and Psychophysical Effects of Lysergic Acid Diethylamide
by E. Jonathan Arnett (1996, Whittier College)

[Full text and references at]

Long-term perceptual disorder.

An aspect of long-term effects to LSD which has only recently garnered attention is the phenomenon known as post-hallucinogen perceptual disorder (PHPD). In this condition, users of LSD report long-term acute visual disturbances after the immediate effects of LSD have dissipated. This category includes continuous visual disturbances (Anderson & O'Malley, 1972) and has been recently proposed as the controlling paradigm for the commonly observed, short-lived "flashback" (Abraham & Aldridge, 1993).

In its chronic, persistent form, PHPD has been found to be a long-term, predominantly visual disorder with incidences ranging from fractions of a second up to five years in duration (Abraham, 1983). It has been described as "like living in a bubble under water. . . . [with] trails of light and images following movement of their hands, and [subjects] often describe living in a 'purple haze'" (Smith & Seymour, 1994, p. 146). Shades of Jimi Hendrix?

The literature is scanty, and early examples of this phenomenon must be teased from the various other labels under which they had been previously placed, but it is possible to find reports of PHPD, for they appeared as early as 1954 by Sandison, Cooper, and Whitelaw, and 1955 by Elkes, Elkes, and Mayer-Gross and by Cooper (Abraham & Aldridge, 1993; Madden, 1994). Reviews by Smith and Seymour (1994) and Abraham and Aldridge (1993) state unequivocally that PHPD may manifest itself after only one dose of LSD. A manifestation of PHPD other than the visual dimension is anxiety, even to the point of panic, with affective depression (Abraham & Aldridge, 1994; Cohen, 1966; Cohen & Ditman, 1963; Madden, 1994; Robbins, et al., 1967; Rosenthal, 1964).

A case report of a 15-year-old boy with a possible case of PHPD is provided by Kaminer and Hrecznyj (1991). The subject used LSD on a daily basis for 6 months before admission to an inpatient treatment facility. He admitted constant perceptual disturbances over the previous 6 months, including colored-dot patterns, white trails behind moving objects, halos around objects, "like a television screen with multiple transmission disturbances" (p. 173), and occasional auditory hallucinations consisting of unintelligible whispers. Flashbacks consisting of illusions of movement and halos around objects occurred and declined in frequency over time, as did the auditory disturbances. However, even after the patient was discharged for 9 months, the visual phenomena continued to persist.


Although the possibility exists that they may be inherently bound to PHPD, flashbacks may be discussed separately due to their more transitory nature. The flashback phenomenon is the subject of much research, not to mention idle speculation and rumor. A flashback may be defined as a (usually) brief recurrence of the psychedelic effects of LSD after the acute pharmacologic effects have dissipated and relative normalcy has been reestablished (Heaton, 1975). It is this relatively normal period which expressly differentiates flashbacks from other adverse reactions, such as extended psychotic reactions and bad trips (Shick & Smith, 1970).

When LSD was first being used, the incidence of flashbacks was relatively rare. For example, Cohen and Ditman (1963) reported two cases with patients who used LSD as an adjunct to therapy, Frosch et. al (1965) reported three cases in schizophrenics, and Leuner reported a case in 1965. However, when LSD escaped the psychiatrist's office and went to the streets where untrained, inexperienced people began to use this powerful hallucinogen, reports of flashbacks began to increase.

The percentage of LSD users who experience flashbacks is unclear, though. Blumenfield (1971) conducted a study with Air Force trainees in which he found that 94 out of 431 (21.9 %) trainees who were identified as having a history of drug abuse had had flashbacks. (It should be noted that five subjects denied LSD use and attributed their flashbacks to marijuana.) Ungerleider, Fisher, Goldsmith, et. al. (1968) sent a questionnaire to 2,700 psychiatrists, general practitioners, internists, psychologists, and psychiatric residents in the Los Angeles area. Of the 1,584 responses, 428 had seen adverse consequences from LSD, and 26% reported that over half of their LSD patients had experienced flashbacks. Horowitz (1969) reported that 7 of 25 subjects who reported chronic LSD use (defined as more than 15 "trips") had flashbacks. A chi-square test did not reveal a statistically significant difference, however. As a purely subjective matter of comparison, Horowitz also asked elder hippies in the Haight-Ashbury district of San Francisco for estimates of flashback incidences among the hippie population. Their admittedly conservative estimate of flashback occurrence was that flashbacks were experienced by only 5% of LSD users--a considerably lower rate of incidence than empirical research would indicate.

Just as there is no single experience inherent in every LSD trip, there is no universal type of flashback experience, but Shick and Smith (1970) found three categories of flashback: the perceptual, somatic, and emotional. The perceptual reaction is the most commonly reported type of flashback. In this type of recurrence, the visual effects of LSD become apparent. Examples include extra-intense color perception, superimposition of geometric patterns, objects changing shape, flowing, or melting, shiny or rainbow-hued halos around objects, and objects shimmering or outright vibrating (Kaminer and Hrecznyj, 1991; Horowitz, 1968; Shick and Smith, 1970). Visualization of entire objects is also possible, as evinced by Horowitz's Patient C, who had a chronic hallucination of an iguana, and the subject in his first case study, who visualized a brown or black scorpion on his hand.. It is worth noting that many LSD users do not attach negative connotations to perceptual flashbacks, but in fact refer to them as "'free' LSD trips" (Shick and Smith, 1970, p. 15).

The second type of flashback is the somatic flashback. In this type of recurrence, the user has an occurrence of altered bodily sensation. This reportedly is often upsetting to the subject, since many of these reactions mentioned occur after a bad trip and include numbness and pain (Shick and Smith, 1970).

The third type of flashback is the emotional flashback. This type of flashback is marked by recurrence of disturbing emotions. These are similar to the somatic flashback in that they most often occur after "bad trips" and cause extreme anxiety to the subject. Consideration of or attempts at suicide may even result from the extreme dysphoria produced by this event (Shick and Smith, 1970).

It is worth noting that no mention was made of any sort of positive emotional flashback state. This is curious when one considers the case of the LSD users who consider their perceptual flashbacks positively as "free trips." This group of users do not appear to suffer from any adverse emotional states, but neither are they reported as having any positive emotional flashbacks in spite of their otherwise sunny outlook on flashbacks. This may be due to one of two factors or a combination of both. The first possibility is that any positive affective states which may arise from an emotional flashback are attributed to incidental factors by subjects--e.g.: "The sun is shining, and it's great to be alive!"--whereas a sudden downswing in mood is easily noticeable in relation to everyday life. The second possibility is that LSD users have been conditioned tooperate in a positive (or at least neutral) affective state. The latter possibility is discussed further under the heading of passivity. Further research in this area may prove enlightening.

The causes of flashbacks are ambiguous, and various theories have been proposed to explain their occurrence, but none is all-encompassing. The release theory suggests that toxic effects of LSD change neurophysiological functioning and disinhibit visual imagery formation. This is supported by the congruence of LSD-induced hallucinations with those produced by other causes, such as electrical stimulation of the brain and migraine (Blacker, Jones, Stone, and Pfefferbaum, 1968; Horowitz, 1964, 1968).

Another possible physiological explanation was reviewed by Rosenthal (1964). He reviewed the possibility that perceptual flashbacks may be caused by changes within the retina or optic nerve pathways, but came to no definite conclusion. The possibility also exists that the eye and its properties (tears, mucus, intraocular arteries, the shape of the retina, arterial pulsations) may be the sources of visual distortions (Abraham, 1983, 1984; Giannini, 1994).

The deconditioning theory suggests a similar mechanism, albeit one that is not dependent upon physiological changes. In this case, Keeler, Reifler, and Liptzin (1968) noted that once a sensation has been noticed, it is more difficult to disregard a similar sensation. This presumably leads to the alteration of attention mechanisms and thereby disinhibition of visual imagery formation. Heaton (1975) pointed out that labeling a state as a flashback sets expectations regarding what is to come and directs attention toward those features, thereby creating a self-fulfilling prophecy (Heaton and Victor, 1976). Horowitz (1969) suggested that unpleasant flashbacks may be an automatic attempt at desensitization to disturbing images which arose on the initial LSD trip.

The psychodynamic theory considers both cultural and personal factors present in imagery. This should work hand in hand with the previously mentioned theories to explain some of the types of things seen in flashbacks. For example, Horowitz (1969) states that in the hallucinogenic drug community, imagery is highly valued and is therefore concentrated upon and reinforced. This emphasis may have an effect of tending to encourage perceptual flashbacks among LSD-using members of this group (Shick and Smith, 1970). Another dimension of the psychodynamic theory is the state of mind in which the user took LSD. Horowitz (1969) suggests that unpleasant flashbacks occur after bad trips because the mind is attempting to work out the traumatic experience which occurred during the trip and that once those repressed ideas are worked through or a positive relationship is established with them, the dysphoric flashbacks disappear. An example of this may be Horowitz's Patient C, who saw an iguana in his flashbacks. At first, the iguana was threatening, but it became a friendly creature over time and no longer frightened the subject.

Another theory regarding the origin of LSD flashbacks is that they are precipitated by stress. Blumenfield (1971) used this argument to provide an explanation for the incidences of flashbacks in Air Force basic trainees; however, Stanton and Bardoni (1972) conducted a study in which they examined the number of reported flashbacks among populations of Army recruits entering and leaving Vietnam and found that stressors such as exposure to combat had no effect on the incidences of flashbacks among the soldiers. It is therefore doubtful that stress has a great effect on incidences of flashbacks.

In spite of the uncertainty surrounding other proposed precipitants of flashbacks, a commonly recognized stimulus is marijuana. Many reports (Favazza & Domino, 1969; Shick & Smith, 1970; Smith, 1968; Stanton, Mintz, & Franklin, 1976; Tennant & Groesbeck, 1972; Weil, 1970) have linked marijuana and flashbacks. This appears to be the most promising angle to be pursued, but as Abraham (1983) points out, research has not been systematic. Further research is needed.