In 2018, a team at Imperial College London tracked more than six hundred people from one week before taking a psychedelic until a month afterward. They wanted to know what predicts how the experience turns out. The answer was not the dose. It was not the location either. What protected most strongly against a difficult experience was the state the person arrived in (Haijen et al., 2018).
That finding put numbers on something the Andean tradition had been organizing long before. Someone who prepares is not satisfying a prerequisite to the ceremony. They are already in it.
Preparing for a San Pedro ceremony narrows four channels at once: what enters through the body, what enters through information, what enters through relationships, and what enters through attention. The food diet is only the first, and it is the one everyone mentions because it is the easiest to list.
This article covers only the stage before. Not the ceremony, not integration. What happens beforehand, which is where much of the rest gets decided.
Grandfather Wachuma and the lineage that holds the ceremony
San Pedro is the name that arrived with the colony. In the Andes it is called wachuma or huachuma, and those who work with it call it Abuelito, Grandfather. It is a columnar cactus, Echinopsis pachanoi, that grows slowly and vertically for years before reaching the size at which it is considered medicine.
One distinction is worth making, because almost nobody makes it. Wachuma's documented root lies in the curanderismo of northern Peru, where the healer's mesa has organized the work for centuries. Bussmann and Sharon (2006) recorded 510 medicinal species in that region and described it as the health axis of the Andean world, with roots reaching back at least to the Moche period. That is the coastal current.
The other current comes from the highlands. The Q'ero people, in the provinces of Paucartambo and Quispicanchi in Cusco, on the slopes of Ausangate, preserve a body of ritual practice that Peruvian anthropology documented beginning with the 1955 expedition of the Universidad Nacional San Antonio Abad, led by Óscar Núñez del Prado (Flores Ochoa et al., 2005). Their ritual specialists are called paqos. They work with the mesa, with khuyas, with k'intus of coca, with the despacho as offering, and with a living relationship to the Apus and Pachamama. In 2007 the Peruvian state declared that heritage a National Cultural Patrimony.
The lineage that holds ceremonies at Dynamis is Q'ero. Cesar, the paqo who leads them, works from within that tradition and is the one who represents it in our space. My role is a different one and I want that clear: I hold the clinical container, the screening beforehand, and the integration work afterward. I do not lead the ceremony and I do not represent a lineage that is not mine. That both things coexist in the same plant medicine retreat, each in its own place and without crowding the other, is exactly the point.
Pharmacologically, mescaline does not behave like the other classic psychedelics. Along with acting on the 5-HT2A receptor, it has adrenergic and dopaminergic activity (Vamvakopoulou et al., 2023). That, combined with a duration that can stretch across most of a day, explains why it asks more of the body than other medicines and why physical preparation carries so much weight here.
What the research found about preparing
Leary, Metzner, and Alpert wrote in 1964 that the experience depends on set and setting: inner state and context. For decades that circulated as a repeated intuition with no hard data behind it. In 2018 it was tested in a prospective design, measuring people before and after rather than asking them to remember.
The three factors that emerged (Haijen et al., 2018):
- Set. Feeling prepared, open, in good spirits, and low in anxiety right before dosing. This was the strongest predictor of having fewer challenging experiences, with a considerably larger effect than dose.
- Clear intention. Predicted mystical-type experiences, which in turn were associated with greater well-being measured at two and four weeks afterward.
- Setting. The item that loaded highest on this factor was not the physical space. It was the relationship with the people who would be present during the experience.
That last point tends to surprise people. Most choose a retreat based on photographs of the space. The data suggest what matters more is how much trust you have in the person holding the room before the medicine takes effect.
Look at what the set factor is made of: prepared, open, in good spirits, unanxious, not chewing on loose ends. None of that gets assembled on the morning of the ceremony. It gets built in the weeks before, through the four channels that follow.
Screening: the part no serious space skips
The only modern safety data we have on mescaline comes from the laboratory. Klaiber and colleagues (2024) analyzed two double-blind, placebo-controlled trials: 48 participants, 96 administrations, doses from 100 to 800 mg. Positive subjective effects outweighed negative ones at every dose, and systolic blood pressure stayed below 180 mmHg in all participants.
That result is encouraging and it needs to be read in full. It says safe in a controlled clinical setting, with healthy, previously screened participants. Lifting that conclusion out of context and applying it to any ceremony is the mistake this article exists to prevent.
Personal and family psychiatric history
The most widely cited safety guidelines in the field recommend excluding people with a personal or family history of psychotic or bipolar disorders (Johnson, Richards, & Griffiths, 2008). We ask about family and not only about you because vulnerability can be present without ever having expressed itself. If someone tells me in an intake interview that a sibling had a psychotic episode at twenty, that changes the conversation even if the person in front of me has never had a symptom.
Heart, blood pressure, and the adrenergic profile
Because of that adrenergic activity, mescaline raises blood pressure and heart rate steadily over hours rather than in a brief spike. A cardiovascular review beforehand is not paperwork. With uncontrolled hypertension, arrhythmias, prior cardiac surgery, a pacemaker, or pregnancy, each case is evaluated individually and sometimes the honest answer is no.
Medication and substances
This is the most important part of the article and I will say it plainly. If you take antidepressants, lithium, antipsychotics, or any psychiatric medication, do not taper on your own or because a retreat told you to. That decision belongs to the physician who prescribed it, made with time, and with the real possibility that the conclusion is that this is not your moment.
I state it that flatly because the idea circulates that it is enough to stop the medication a few weeks ahead. Discontinuing an antidepressant in someone with depression carries discontinuation syndrome and relapse risk, and the window of greatest vulnerability can land squarely on the day of the ceremony. No space, ours included, has the standing to ask that of you.
If you arrive with a history of problematic substance use, the conversation is different and longer. That is the terrain of our 9Seeds program, and the work often begins there rather than in a ceremony.
All of this gets discussed beforehand, in a real interview with someone who knows what they are listening for. At Dynamis that happens in an integrative psychology session or a preliminary conversation, never in a form that autocompletes.
First channel: the diet of the body
The traditional window is fifteen days, with a tighter adjustment in the final three. That long runway is not arbitrary. It gives the digestive system time to settle and, more importantly, it installs the habit of paying attention to what goes in.
Across the fifteen days, out go alcohol, red meat and pork, cured meats, fast food and ultra-processed products, sodas, fried and heavily spiced dishes, refined sugar and salt. Dairy and fermented foods get reduced.
What carries you through: white meats, cooked vegetables, soups, salads, seeds and nuts, seasonal fruit, unrefined sugar, and sea or rock salt. Simple food, which is precisely what most people stop eating when life gets busy.
In the final three days dairy also goes, along with beans and legumes, cruciferous vegetables like broccoli, cauliflower and cabbage, fermented and preserved foods like pickles, olives, kombucha and kefir, and citrus. Eating turns soft: steamed vegetables, soups, oat or quinoa porridge, simple pasta with olive oil. Plenty of water, and digestive teas like mint, chamomile, or spearmint.
The reason for that last adjustment is concrete. Every one of those groups produces gas and abdominal distension, and mescaline frequently produces nausea (Klaiber et al., 2024). An inflamed gut turns manageable nausea into an uncomfortable night.
You eat on the day of the ceremony, and this contradicts what many people assume. A full breakfast is essential. Lunch goes light and early, around midday. The final snack, roughly six hours before the start, comes down to soft fruit, an herbal tea, seeds, and a little bread. You arrive with a light digestive system, not an empty one since morning. Fasting all day before a long medicine is a fairly reliable way to arrive depleted.
The tradition also asks for sexual abstinence four days before and four days after. I include it because it is part of the lineage's protocol and leaving it out would be dishonest, and I name it for what it is: a practice of the tradition, without clinical evidence behind it. The same holds for refined salt and sugar. Coming from tradition does not make something invalid. Presenting it as though a clinical trial stood behind it does.
Second channel: the diet of information
This is the one almost nobody writes about and, in my experience, the one that makes the biggest difference for people who live connected.
In the last week before the ceremony you also watch what enters through the eyes and ears: social media, news broadcasts, press, content that leaves the body activated. This is not soft wellness advice. Media exposure is a measurable stressor.
Holman, Garfin, and Silver (2014) studied 4,675 people after the Boston Marathon bombing. They found that six or more daily hours of bombing-related coverage in the following week were associated with higher acute stress than having been physically at the scene. The effect held after controlling for prior mental health, which had been measured before the bombing.
The study measures coverage of collective trauma, not everyday scrolling, and it should not be stretched past that. What it does establish solidly is that the content we consume is not neutral background. It enters the nervous system.
Porges (2011) coined the term neuroception for the process by which the body evaluates whether an environment is safe before the mind has a chance to weigh in. It is faster than thought. If you spend the week beforehand feeding that system on threat, you arrive with your neuroception calibrated to alert, and your body will read the Maloca through that lens even though the Maloca is safe.
The practical instruction is simple: turn down the volume on news and social media for those seven days, and replace it with material that leaves something rather than taking something. Music, reading, walks, conversations that do not leave you churning.
Third channel: the diet of relationships
The week before is also protected by avoiding sharp confrontations and arguments that leave the body loaded. And there is a second part, less comfortable: looking at who you need to forgive, and what you need to forgive in yourself.
It sounds like spiritual advice and it has physiological backing. Witvliet, Ludwig, and Vander Laan (2001) measured 71 people as they alternated between rehearsing a real offense and practicing forgiveness imagery toward that same offender. Rehearsing the grudge significantly raised heart rate, blood pressure, and skin conductance relative to baseline. The forgiveness imagery did not produce that activation.
Translated into what matters here: arriving with open accounts you keep chewing on means arriving with the sympathetic system switched on. And Haijen's set factor, the one that protected most against a difficult experience, is composed of exactly the opposite.
The tradition did not ask for forgiveness out of moral virtue. It asked because someone at war with another person arrives at war with themselves, and Grandfather works with what he finds.
This is not about resolving the relationship or calling anyone. It is about stopping the work of holding the story in your body for those days.
Fourth channel: intention, written by hand
Intention and expectation are not the same thing, even though they sound alike. An expectation is a picture of the outcome. An intention is a direction.
In the Haijen study, the clear intention component was the one that pushed toward mystical-type experiences. And in an international survey of 452 people who had taken mescaline, what correlated with reported improvement was not the perceptual effects but the moments of psychological insight during the experience (Agin-Liebes et al., 2021). That study is retrospective self-report rather than a controlled trial, and that is worth holding in mind. Even so, it points in the same direction as what I see clinically.
The exercise is simple and the tradition had already solved it: write your intention on a small piece of paper, by hand, and carry it into the ceremony. Frame it as a question. What do I need to look at, release, understand, heal.
Most people write something close to "I want the anxiety to go away." That is an expectation. The version that works usually sits one layer beneath: "I want to see what the anxiety is protecting me from."
A woman I accompanied arrived intending to forgive her father. She left the ceremony without having thought about him once. What surfaced instead was how much energy she had spent over two decades holding that story in place. The intention was not fulfilled. It did something better: it took her to the right place.
What to bring, and why
Every item on this list answers to a practical or ceremonial reason. They are worth understanding, because arriving without some of them can cost you comfort across many hours.
- Warm layers, a blanket, comfortable clothes. The medicine can lower body temperature. Being cold for hours ruins an experience that was going well.
- Yoga mat, cushion, towel. You will spend a long time on the floor.
- A small bucket or basin and tissue. Purging is part of the work and it is not a failure.
- Shoes that slip on and off easily. You will step in and out of the space several times.
- A water bottle at room temperature. Very cold water sits badly during the experience.
- Notebook and pen. What surfaces during the ceremony blurs quickly if it is not written down.
- A small candle, two flowers (one white or yellow, one red, orange or pink), an artisanal sweet, and an object of symbolic value to your path. These belong to the mesa and to the offering within the paqo's work.
- Soft fruit or bread to share at the end. The closing is collective, and eating together is part of landing.
- A change of clothes for the following day.
Two instructions that usually get forgotten. No perfume or strongly scented products: olfactory sensitivity sharpens during the experience, and penetrating chemicals bother the whole group, not only the person wearing them. And do not drive that day or the next. Staying in the cabins, rather than driving in from somewhere else in Guanacaste, solves much of this on its own, which is why the structure of the retreat treats the following day as part of the program.
Schedule your integration session before the ceremony, not after. The next day you will be in a state where organizing things is not your strength.
What preparation cannot do
Preparing well does not guarantee a pleasant experience. You can have a difficult night having done everything right, and that does not mean you failed. Preparation does not control the outcome. It shifts the odds and, more than anything, it changes your capacity to hold whatever shows up.
I also want to be straight about the state of the evidence. Of the classic psychedelics, mescaline is the least studied. Vamvakopoulou and colleagues (2023) say it without hedging: the evidence base is still insufficient for clinical recommendations, and modern controlled studies are needed. There are interesting signals. There are no certainties. Anyone promising you results with this cactus is selling something.
When someone arrives at the seven acres of tropical dry forest, something starts coming down before the ceremony begins. That is already preparation, even when it does not feel like it. The Maloca is not where the process starts. It is where a process that has been walking toward you for two weeks meets the medicine.
Frequently asked questions
How long before a San Pedro ceremony should I start preparing?
The food diet begins fifteen days out, with a stricter adjustment in the final three. The information and relationship diets cover the last week. Medical and psychological screening should happen with even more lead time, ideally when you book, because its outcome can change the decision.
What can I not eat or drink before taking Wachuma?
For fifteen days: alcohol, red meat and pork, cured meats, ultra-processed food, sodas, fried dishes, refined sugar and salt. In the final three days, dairy, beans, cruciferous vegetables like broccoli and cabbage, fermented foods, and citrus also come out, because they produce gas and worsen nausea.
Do I need to fast on the day of the ceremony?
No. You eat a full breakfast, a light early lunch, and a final snack about six hours before the start: soft fruit, herbal tea, seeds, a little bread. The goal is to arrive with a light digestive system, not one weakened by a long fast.
Can I participate if I take antidepressants?
It requires individual evaluation, and that evaluation belongs to the physician who prescribed the medication, not to a retreat. Never taper on your own. In some cases the conclusion is that it can be done with adjustments and support. In others, that this is not the time. Both answers are legitimate.
Who should not take San Pedro?
People with a personal or family history of psychotic or bipolar disorders, per the field's most established safety guidelines. Also anyone with uncontrolled cardiovascular conditions, prior cardiac surgery, a pacemaker, or pregnancy. And anyone in an acute crisis that needs stabilization before expansion.
Before you book a date
The cactus takes years to grow large enough to be medicine. Nobody rushes that. Preparation is the stretch of time in which a person does something similar: letting something mature before cutting it.
What interests me most about all of this is that the lineage and the research arrived at the same place by different roads. The paqo asks for diet, silence, settled accounts, and a clear question written on a piece of paper. The prospective study finds that set, intention, and the relationship with the person holding the space are the variables that carry the most weight. Neither had to give ground for them to agree.
If you are considering sitting with Grandfather, the first step is not booking. It is an honest conversation about your history, your health, and your moment. Sometimes that conversation ends in a yes. Sometimes it ends in a not yet, and that is also a good outcome.
Write to us and let's talk before you decide anything: schedule a preliminary conversation with Dynamis.
If you have already walked that part and want to see when the next opportunity is, look at upcoming retreat dates in Tamarindo, Guanacaste.
References
Agin-Liebes, G., Haas, T. F., Lancelotta, R., Uthaug, M. V., Ramaekers, J. G., & Davis, A. K. (2021). Naturalistic use of mescaline is associated with self-reported psychiatric improvements and enduring positive life changes. ACS Pharmacology & Translational Science, 4(2), 543-552. https://doi.org/10.1021/acsptsci.1c00018
Bussmann, R. W., & Sharon, D. (2006). Traditional medicinal plant use in Northern Peru: Tracking two thousand years of healing culture. Journal of Ethnobiology and Ethnomedicine, 2, 47. https://doi.org/10.1186/1746-4269-2-47
Flores Ochoa, J. A., Núñez del Prado B., J. V., & Castillo Farfán, M. (Eds.). (2005). Q'ero, el último ayllu inka: Homenaje a Óscar Núñez del Prado y a la expedición científica de la UNSAAC a la nación Q'ero en 1955 (2nd ed.). Fondo Editorial de la Facultad de Ciencias Sociales, UNMSM; Instituto Nacional de Cultura.
Haijen, E. C. H. M., Kaelen, M., Roseman, L., Timmermann, C., Kettner, H., Russ, S., Nutt, D., Daws, R. E., Hampshire, A. D. G., Lorenz, R., & Carhart-Harris, R. L. (2018). Predicting responses to psychedelics: A prospective study. Frontiers in Pharmacology, 9, 897. https://doi.org/10.3389/fphar.2018.00897
Holman, E. A., Garfin, D. R., & Silver, R. C. (2014). Media's role in broadcasting acute stress following the Boston Marathon bombings. Proceedings of the National Academy of Sciences, 111(1), 93-98. https://doi.org/10.1073/pnas.1316265110
Johnson, M. W., Richards, W. A., & Griffiths, R. R. (2008). Human hallucinogen research: Guidelines for safety. Journal of Psychopharmacology, 22(6), 603-620. https://doi.org/10.1177/0269881108093587
Klaiber, A., Humbert-Droz, M., Ley, L., Schmid, Y., & Liechti, M. E. (2024). Safety pharmacology of acute mescaline administration in healthy participants. British Journal of Clinical Pharmacology. https://doi.org/10.1111/bcp.16349
Leary, T., Metzner, R., & Alpert, R. (1964). The psychedelic experience: A manual based on the Tibetan Book of the Dead. University Books.
Porges, S. W. (2011). The polyvagal theory: Neurophysiological foundations of emotions, attachment, communication, and self-regulation. W. W. Norton.
Vamvakopoulou, I. A., Narine, K. A. D., Campbell, I., Dyck, J. R. B., & Nutt, D. J. (2023). Mescaline: The forgotten psychedelic. Neuropharmacology, 222, 109294. https://doi.org/10.1016/j.neuropharm.2022.109294
Witvliet, C. V. O., Ludwig, T. E., & Vander Laan, K. L. (2001). Granting forgiveness or harboring grudges: Implications for emotion, physiology, and health. Psychological Science, 12(2), 117-123. https://doi.org/10.1111/1467-9280.00320
