Hallucinogens are used in several distinct ways: in supervised therapeutic settings to treat mental health conditions, in traditional indigenous ceremonies, as recreational substances, and increasingly in tiny “microdoses” aimed at boosting focus and mood. The method, dose, and context vary dramatically depending on the purpose, and each carries different risks and timelines.
Two Main Categories of Hallucinogens
Hallucinogens fall into two broad groups. Classic hallucinogens include LSD, psilocybin (the active compound in “magic mushrooms”), mescaline (found in peyote and San Pedro cacti), and DMT (the psychoactive ingredient in ayahuasca). These all work primarily by activating serotonin receptors in the brain, specifically a receptor called 5-HT2A. When these receptors are stimulated, they trigger changes in how nerve cells communicate, leading to altered perception, visual distortions, and shifts in thought and emotion.
Dissociative drugs are the second category. These include PCP, ketamine, DXM (found in some over-the-counter cough medicines), and salvia divinorum. Rather than amplifying sensory input, dissociatives create a feeling of detachment from the body and environment. Ketamine is the most widely used of this group in medical settings, where it’s still employed as an anesthetic.
Traditional and Ceremonial Use
Hallucinogens have been used in spiritual and healing rituals for thousands of years. Psilocybin mushrooms, peyote, San Pedro cactus, and ayahuasca all have deep roots in indigenous cultures across the Americas. These aren’t casual or recreational experiences. They follow structured traditions with specific rules about preparation, setting, and guidance.
Ayahuasca ceremonies in the Amazon, for example, are conducted at night and led by a shaman who prepares the brew and provides spiritual support throughout the experience. The brew itself combines two plants: one containing DMT and another containing compounds that allow DMT to become active when swallowed. The result is a psychedelic experience lasting four to six hours. Participants typically follow a restricted diet before and after the ceremony, avoiding alcohol, cheese, and fermented foods. Both the preparation leading up to the ceremony and the integration period afterward are considered essential parts of the process, not just the psychedelic experience itself.
People who seek out these ceremonies are generally looking for personal growth, emotional healing, or treatment of psychological struggles. The intentional, supervised, and spiritual setting is thought to shape the experience in ways that a casual or unstructured use would not.
Therapeutic and Clinical Use
Researchers are now studying hallucinogens as treatments for depression, PTSD, substance use disorders, and end-of-life anxiety. Most clinical trials use psilocybin, typically at a fixed dose of 25 milligrams of synthetic or extracted psilocybin for a standard session, with higher doses of 35 mg or more reserved for specific protocols. These sessions take place in controlled environments with trained therapists present before, during, and after the experience.
A therapeutic session looks nothing like recreational use. Patients typically lie on a couch, wear eyeshades, listen to music, and are encouraged to turn their attention inward. The psilocybin experience lasts roughly five hours, during which therapists remain present but largely let the experience unfold. Preparation sessions happen beforehand to build trust and set intentions, and integration sessions follow to help patients process what they went through. The FDA has issued draft guidance for how these clinical trials should be designed, signaling that the agency takes the therapeutic potential seriously.
That said, no classic hallucinogen is currently FDA-approved for any psychiatric condition. In 2024, the FDA rejected an application for MDMA-assisted therapy for PTSD, and the company behind it is now planning additional trials. Several states are moving toward regulated access models, where psilocybin or other psychedelics could be used in supervised, licensed facilities rather than at home.
Microdosing
Microdosing involves taking a fraction of a recreational dose, typically one-twentieth or less, on a regular schedule. For LSD, that means roughly 6 to 25 micrograms. For psilocybin mushrooms, it’s about 0.1 to 0.5 grams of dried material. At these levels, the goal is not to experience any perceptual changes at all.
The most common schedule is dosing once every three days, based on the idea that each microdose has a residual effect lasting a day or two. In practice, people vary widely in their routines. One study found that participants microdosed about five times over the study period, with an average of nearly seven days between doses. People who microdose report improvements in creativity, focus, productivity, mood, and social ability, though it’s worth noting that most of this evidence comes from self-reports rather than controlled experiments. Microdosing gained particular popularity in the technology sector, where it’s been promoted as a productivity tool.
How They’re Physically Taken
The route of administration depends on the substance. LSD is most often taken by mouth, placed on the tongue as a small square of blotter paper, a tablet, or a liquid drop. Psilocybin mushrooms are eaten whole (fresh or dried), brewed into tea, or sometimes ground into capsules. Mescaline is consumed by eating slices of peyote cactus or drinking a prepared extract. Ayahuasca is always consumed as a brewed liquid.
DMT in its pure form is typically inhaled as a vapor or smoke, which produces a very short but intense experience. When combined with an MAO inhibitor in ayahuasca form, it becomes orally active and lasts hours instead of minutes. Ketamine can be injected, snorted, or taken as a lozenge. Salvia is usually smoked. Some tryptamine compounds have also been used intranasally or sublingually (under the tongue), with each route affecting how quickly and intensely the substance takes hold.
How Long the Effects Last
Duration varies significantly across substances. A controlled crossover study comparing three classic hallucinogens in healthy participants at equivalent doses found clear differences. Psilocybin had the shortest duration, averaging 4.9 hours. LSD lasted a mean of 8.2 hours. Mescaline was the longest at 11.1 hours. Mescaline’s extended duration comes partly from its slower absorption, as it takes longer to reach peak concentrations in the blood even though its elimination half-life is similar to LSD’s (about 3.5 hours for both).
Smoked or vaporized DMT is on the opposite end of the spectrum, producing effects that peak within minutes and largely resolve in 15 to 30 minutes. Ayahuasca, because it delivers DMT through the digestive system with a compound that slows its breakdown, extends that window to four to six hours. Ketamine’s effects are also relatively brief, typically lasting 45 minutes to an hour when used in clinical settings, though aftereffects can linger longer.
Risks and Long-Term Effects
The most commonly discussed long-term risk specific to hallucinogens is hallucinogen persisting perception disorder, or HPPD. This condition involves the return of visual disturbances that first appeared during a hallucinogenic experience, occurring long after the drug has left the body. Symptoms are primarily visual: trailing images, halos around objects, intensified colors, or geometric patterns in the visual field. The DSM-5 estimates a prevalence of about 4.2% among hallucinogen users, though reliable numbers are difficult to pin down.
HPPD comes in two recognized forms. Type I involves brief, intermittent flashbacks. Type II is more persistent and pervasive, with symptoms that can be long-lasting or only slowly reversible. The distinction between the two hasn’t been formally adopted in diagnostic manuals and remains debated among researchers.
In the shorter term, hallucinogens can cause intense anxiety, confusion, and paranoia during the experience itself, commonly called a “bad trip.” Dissociative drugs carry additional risks including impaired coordination and, at high doses, dangerous changes in heart rate and blood pressure. The controlled trial comparing mescaline, LSD, and psilocybin found that all three were generally tolerable, though mescaline caused slightly more adverse effects in the 12 to 24 hours following the session than the other two.