After consuming San Pedro, most people start to feel the effects within 15-40 minutes, but it could take up to three hours to peak. Coming down can take another three hours, and the whole experience usually lasts 10 hours or so. San Pedro also usually leaves a lasting afterglow, which can make it difficult to sleep after the effects wear off. [1]

Many people are surprised at how different San Pedro (and mescaline, in general) is from other psychedelics they’ve tried. San Pedro can leave you feeling relaxed and in control, for instance, even if you’re tripping heavily. [2][3][4][5][6] One user compared its effects to MDMA, but felt they were “more amazing.” “Mescaline didn’t feel like rolling [being high on MDMA],” he said, “Rolling felt like mescaline.” The same user went on to say that it was “like all the best effects from all the drugs all put into one… the great body feeling and incredible empathy and understanding of ecstasy… the focus and energy and drive of acid… the journey effect that I always enjoyed from shrooms… It was the soberest we had ever felt in our life.”[4]

When the effects of San Pedro first hit, it’s common to feel drowsy or dizzy, often with a sense of tingling or electricity in the veins.[7][5] Nausea, vomiting, and perspiration are also common on the come-up.[8]

San Pedro usually produces visual effects, including whirlpools of colored light, flashes in the peripheral vision, kaleidoscopic patterns, and white, ghostlike outlines around people.[8] “Out-of-body” experiences are also common, as is synesthesia (e.g. “feeling” and “smelling” sights and sounds), mild depersonalization, and distortions of spatial awareness.[9][10][8][11][12] At the same time, ordinary things around you can appear more interesting, beautiful, and amazingly mystical—qualities that define the mescaline experience.[13]

All of this often culminates in a clear and connected thought, self-realization, empathy, and euphoria. However, “bad trips” and dysphoric symptoms may be more common among people who don’t pay attention to set and setting and/or have histories of mental illness.[14]

For safety and ethical reasons, it’s best to experience San Pedro in the context of a ceremony with a qualified curandero (healer), which are becoming more common in the West, in addition to the growing number of retreats in South America.

These ceremonies often last all night and are repeated over several days. In addition to San Pedro, curanderos may use other plants, including other cacti and succulents, lycopods (clubmosses), datura, brugmansia, and Isotoma/Hippobroma longiflora (aka the “Star of Bethlehem”).[8][7][15][16][17]

Ceremonies traditionally center on a “healing altar” or mesa, covered with “power objects”—ancient artifacts, staffs, stones, crosses, images of saints, and more. These are usually sorted into three zones or fields (campos) according to their energy alignment—positive (life-giving), negative (death-taking), or neutral.[8][15][18]

Before ingesting San Pedro, ceremony participants are “purified” with a bath of “spiritual flowering” or baño de florecimiento, and often snort tobacco. After, each person is diagnosed and treated by the healer, which might involve the invocation of spirits from both Andean and Christian cosmology and passing a sword or staff over the patient in the form of a cross.[8][19] Sometimes a guinea pig is passed over the body instead, then killed and dissected to determine the activity or source of an illness.[19][15]

Whatever takes place in the ceremony, cures are generally attributed to the plant as opposed to the healer or shaman. The healer is considered a facilitator, “activated” by the cactus to stimulate “the five senses of the patient in a familiar cultural environment” using music, perfumes, symbols, and other ritual elements.[8]

In a traditional ceremony, distinctions between the body and mind go by the wayside. Shamans may recognize the medical causes of disease—and even integrate pharmaceuticals into practice—but they’ll generally look beyond the strictly physical for an underlying spiritual basis for the illness.[8][1][16] Contemporary practitioners tend to frame this in psychosomatic terms, viewing “illness as a thoughtform” and the “guidance of the plant” as helping patients “to see the origin of [their] own illness without judgments or interpretations from others.”[20][21]

Pharmacology
San Pedro contains highly variable concentrations of mescaline, which is densest in the outermost, greenest layer of the cacti’s flesh. [9][7][22][23][24][25][26][27] Like MDMA and 2-CB, mescaline is a phenethylamine, which puts it in a different class of psychedelics than the tryptamines (psilocybin, DMT) and ergolines (LSD, LSA). The cactus also contains hordenine, anhalonidine, anhalonine, trichocerine, tyramine, and several substituted phenethylamines besides mescaline.[22][26] While their effects are thought to be secondary or negligible compared to mescaline’s, they may account for some of San Pedro’s purported medicinal benefits. Hordenine, for example, is an antibiotic, and anhalonidine has a mildly sedative effect.[28]

Dive deeper into San Pedro’s full spectrum of active ingredients, including mescaline, anhalonidine, and anhalonine in our recent article.

Receptor binding
Mescaline binds to virtually all serotonin receptors in the brain but has a stronger affinity for the 1A and 2A/B/C receptors. It is structurally similar to LSD and often used as a benchmark hallucinogen when comparing psychedelics.

Like nearly all hallucinogens, the psychedelic effects of mescaline are likely due to its action on serotonin 2A receptors.[29]

Mescaline also has an affinity for the dopamine receptors, either as a selective reuptake inhibitor or as a dopamine receptor agonist.[30]

There’s no way to tell how much mescaline a cactus contains just by looking at it, which can make finding the right dosage tricky—especially given San Pedro’s variability. Just 50g dried cactus material might contain as little as 150mg of mescaline (a threshold dose) or as much as 1150mg of mescaline (a potential overdose).[27] It’s best to work with a qualified San Pedro ceremony facilitator to ensure you get the right dose.

Potential Benefits
San Pedro has long been considered a powerful agent for healing and change, making it a central component of the shamanic ceremonies of many indigenous groups in the Americas. For many, a San Pedro journey offers deep insight into the self and the universe, giving one a greater sense of connection and spirituality. Mescaline is also known for fostering compassion and gratitude, while alleviating psychological disorders such as anxiety, depression, PTSD and addiction.

Mescaline has also been shown to help people solve problems, access their creativity, be more environmentally conscious, and improve learning. In its original use, the plant medicine was also used to treat a number of ailments, including snake bites, wounds, skin conditions, and general pain.

Risks
Due to its status as an internationally controlled substance, research into the harm potential of mescaline—especially long-term—has been limited. A lethal dose has never been identified, probably because it’s too high to be taken accidentally.[31] But that doesn’t mean it’s entirely safe. People have died as an indirect result of mescaline use, including suicides and one fatal case from excessive vomiting. That’s why it’s important to monitor dosing closely. According to the Erowid Mescaline Dosage page, the maximum safe amount for a heavy trip is about 500 mg of San Pedro.[32]. However, dosage depends on the consumption method. For pure San Pedro extracts, Erowid indicates the maximum dosage is much lower–somewhere between 75 – 100 mg.

A 2005 study into the ceremonial use of peyote among Native American populations found there to be no detrimental long-term effects. [33] It should be noted, however, that its use in other contexts may not be as safe (remember: set and setting). However, its use in other contexts may not be as safe—later studies have found an association between prior mental health problems and “bad trips.” Stil, mescaline appears to present little risk of flashbacks, or hallucinogen persisting perception disorder (HPPD).[34][35]

Most mescaline goes straight to the liver, so it may not be safe if you have liver problems (although it was given to many chronic, often severely liver-diseased alcoholics in the 1950s and ’60s without any obvious complications).[28] People with colon problems, high blood pressure, heart conditions, diabetes, or mental illness should also be cautious.[20][36] Although peyote (which also contains mescaline) is traditionally consumed by Huichol women during pregnancy, mescaline has been linked to fetal abnormalities and should also be avoided by pregnant or breastfeeding women. [37][38]

San Pedro may not be safe in combination with MAOIs (natural or synthetic), including the antidepressants phenelzine (Nardil) and tranylcypromine (Parnate). Some use MAOIs like moclobemide (Amira, Aurorix, Clobemix, Depnil, Manerix) to enhance the effects or prevent nausea but they may not be safe for everyone’s biochemistry. In fact, MAOIs may actually increase or induce nausea.[39]

It’s possible that non-MAOI antidepressants (such as SSRIs) may dampen San Pedro’s psychoactive effects, but as far we know, combining the two is not physically dangerous.[36]