Acid Flashbacks

Acid flashbacks are one of the long-term effects of LSD use, and can interfere with a person’s daily life even months or years after they use LSD. Scientists still know little about what causes them or how to treat them. Keep reading for more on acid flashbacks.


An acid flashback occurs when a person who has used LSD in the past experiences the effects of acid use, such as hallucinations, without taking the drug again. They can occur days or even years after the person used LSD. Acid flashbacks may occur only once, or they may be persistent and interfere with a person's ability to function in daily tasks.

A person experiencing an acid flashback may see colors or spots that aren’t there or may see things in a distorted way, such as with halos or trails of light. Acid flashbacks more rarely cause people to hear things that aren't real. The person experiencing acid flashbacks may not be able to tell what is real and what is not, and they may feel like they are high on LSD again. Like the effects of LSD, acid flashbacks vary from person to person and are very unpredictable and often frightening.

When acid flashbacks continue and interfere with daily life this is known as hallucinogen-induced persistent perception disorder (HPPD). The most common type of HPPD occurs when a person’s normal vision is often disrupted by flashbacks, such as seeing spots or trails of light frequently, though it can be more serious and interfere with a person’s perception of reality.

Scientists aren't sure what causes acid flashbacks or HPPD, but there are several theories:

  • The brain may be damaged by LSD use, causing it to misfire and send incorrect signals
  • The way the brain functions and perceives information may be changed by LSD use, such as being much more sensitive to light and therefore seeing halos or trails
  • The drug or some portion of it may be stored in the body or brain and released again later

Not everyone who uses LSD has acid flashbacks, but because LSD has very unpredictable effects it's hard to know if a person will have flashbacks and when the acid flashbacks will occur. Some factors that seem to increase the chances of a person having flashbacks include:

  • Heavy or frequent LSD use
  • Bad LSD trips
  • Marijuana use
  • Drinking alcohol
  • Fatigue
  • Stress
  • Existing mental illnesses or personality disorders
  • Use of certain prescription drugs, like anti-depressants
  • Being susceptible to suggestion

These risk factors do not give a clear indication of who will experience an acid flashback, however, since even a healthy person who only uses LSD once may experience acid flashbacks.

There is no cure for acid flashbacks. Some medications, such as anti-seizure drugs, have been used in flashback or HPPD treatment, but perhaps because of the unpredictability of acid flashbacks doctors have not yet found a definite cure for all acid flashback sufferers.


National Institute on Drug Abuse, "Hallucinogens: LSD, Peyote, Psilocybin, PCP" [online]

SAMHSA Health Information Network, "Lysergic Acid Diethylamide (LSD)" [online]

PubMed Central, Canada Medical Association Journal, "Use of anti-epileptic medication in treating 'flashbacks' from hallucinogenic drugs" [online]

ERIC, "LSD Flashbacks: An Overview of the Literature for Counselors" [online], "Drug Flashbacks. II. Some additional findings." [online]

International Bibliographic Information on Dietary Supplements, Record detail, "LSD flashback syndrome exacerbated by selective serotonin reuptake inhibitor antidepressants in adolescents" [online]

Related Article: LSD Long Term Use and Effects >>