Ayahuasca and cancer treatment

Schenberg situates ayahuasca as an Amazonian plant decoction traditionally used by healers for a wide range of purposes and suggests it may have utility in treating some cancers. Earlier reports and ethnographic observations have identified at least nine published cases in which cancer patients consumed ayahuasca during their illness; the cancers reported include prostate, colon, ovarian, breast, uterine, stomach and brain origins. Some of these reports included biochemical markers of improvement (for example, reductions in prostate-specific antigen or carcinoembryonic antigen), while others were ambiguous or subjective, leaving the clinical picture uncertain. The paper therefore sets out to review biomedical and non‑professional literature on ayahuasca with a specific focus on possible relationships to cancer treatment, and to present a theoretical model linking pharmacology, cellular mechanisms and psychosocial factors. Schenberg aims to synthesise available case reports and mechanistic data for the brew's principal active components—mainly N,N‑dimethyltryptamine (DMT) and β‑carbolines such as harmine—and to propose directions for further research into safety and efficacy given ongoing patient interest in this traditional medicine.

The study is a narrative, in‑depth literature review drawing on multiple source types. Searches and data gathering included PubMed and peer‑reviewed literature, books, institutional magazines, conference reports, and online non‑professional texts; the extracted text does not provide a detailed, reproducible search strategy, date range, or inclusion/exclusion criteria. Schenberg integrates clinical case reports (peer‑reviewed and anecdotal), pharmacological and molecular studies, in vitro and in vivo experiments, and anthropological observations to build a multi‑level argument. Because the paper synthesises diverse evidence types, the authors combine descriptive case synthesis with a mechanistic review: summarising the reported clinical cases, reporting measured plasma concentrations and pharmacokinetic observations from human studies where available, and reviewing cellular and molecular data on DMT, β‑carbolines and relevant targets such as the sigma‑1 receptor, MAO enzymes, and other pathways implicated in angiogenesis, apoptosis and metabolic regulation. The review also considers psychosocial dimensions of ritual ayahuasca use (set and setting) and draws on comparisons with other psychedelic interventions in cancer‑related anxiety to contextualise potential therapeutic mechanisms. The extracted text does not report formal risk‑of‑bias assessment or meta‑analytic methods, and many source reports are anecdotal or lack full clinical data.

Schenberg identifies at least nine published case reports in which patients consumed ayahuasca during cancer treatment. These reports came from diverse sources: four in peer‑reviewed articles, one in an institutional magazine, one from internet sources, two presented at scientific conferences (also later mentioned in peer‑reviewed work), and one in a book. Outcomes varied: three cases showed objective improvements by markers such as PSA or CEA, one case was judged worse, and one was considered difficult to evaluate. Independently of objective measures, all patients reported positive subjective effects from the ceremonies. Selected illustrative cases are described in detail. A well‑documented case involved Donald Topping, diagnosed with colon cancer and later metastatic liver disease, who declined chemotherapy after resection and underwent ayahuasca sessions and shamanic healing; his CEA fell to below normal and he remained in remission for a period before dying years later of unrelated causes. Aprile Blake reported subjective resolution of a brain tumour (acromegaly) following multiple ayahuasca sessions with Shipibo healers, though post‑treatment medical examination reportedly did not show significant objective improvement. Robert Forte documented several anecdotes including a prostate cancer patient whose PSA improved and an ovarian cancer patient whose CA‑125 fell from 4,000 to 600 after ayahuasca ceremonies. A peer‑reviewed study identified four cancer patients with mixed outcomes (prostate: no effect; uterine cancer: complete recovery; uterine myoma: worse; stomach cancer: unratable because the patient declined follow‑up exams). Another autobiographical case of a musician described disappearance of detectable breast cancer after multiple healing trips involving ayahuasca and related practices. At the molecular and cellular level, the authors summarise evidence that DMT acts as an agonist at several serotonin receptors and, importantly, binds the sigma‑1 receptor (reported KD ≈ 14–15 µM). Sigma‑1 receptors are intracellular chaperones concentrated at the mitochondria‑associated endoplasmic reticulum membrane (MAM) and are implicated in calcium signalling, mitochondrial function and apoptotic regulation. Schenberg outlines a hypothesis in which DMT, particularly when MAO is inhibited by β‑carbolines in the brew, could modulate ER→mitochondria calcium flux, alter mitochondrial membrane potential, increase reactive oxygen species and trigger apoptosis in cancer cells. DMT at higher concentrations may prompt sigma‑1 translocation to the plasma membrane and modulate multiple ion channels, potentially affecting cell cycle and metastatic behaviours (for example, via NaV1.5 and volume‑regulated Cl− channels). β‑carbolines such as harmine are reviewed as MAO‑A inhibitors that enable oral bioavailability of DMT and as molecules with independent anticancer activities in some models: harmine has induced apoptosis in HepG2 hepatocellular carcinoma cells, reduced proliferation in certain carcinoma and leukemia lines, inhibited tumor angiogenesis in mice, and inhibits DYRK1A kinase (a kinase implicated in resistance to apoptosis). Harmine may also upregulate the glial glutamate transporter EAAT2, potentially relevant for gliomas. Conversely, the authors note conflicting reports about genotoxicity for certain β‑carbolines in cell culture, indicating mixed evidence on safety at the cellular level. Pharmacokinetic data from human studies are summarised: harmine plasma concentrations after ayahuasca vary widely (reported roughly 5.0 ng/mL to 114.8 ± 61.7 ng/mL) and estimated harmine content in ayahuasca studies approximates 1.5 mg/kg—lower than doses used in some rodent cancer studies. Measured DMT Cmax values in volunteers ranged roughly 15.8 ± 4.4 ng/mL to peaks near 32.6 ± 20.96 ng/mL. The authors estimate oral DMT bioavailability after ayahuasca at about 10%–15% but highlight a discrepancy between plasma concentrations and the in vitro affinity for sigma‑1 receptors. To reconcile this, they cite evidence that DMT can act as a substrate for the serotonin transporter (SERT) and be sequestered into cells and vesicles via VMAT2, possibly producing higher intracellular concentrations than plasma levels indicate. DMT is also metabolised to DMT‑N‑oxide and displays rapid tissue uptake and clearance in animal models. On the psychosocial side, ritual ayahuasca ceremonies produce strong psychedelic experiences—visual imagery, intense emotions, spiritual experiences—and the authors emphasise the importance of set and setting. They argue these psychological and ritual factors may contribute to improved quality of life, reduced anxiety and depression, enhanced coping with terminal illness, and potentially indirect effects on survival, citing parallels to guided imagery, music therapy and recent psilocybin trials for anxiety in advanced cancer. Safety observations from earlier psychedelic trials in cancer patients are reported as generally manageable, but the authors caution about risks related to unsupervised use, drug tourism and the legal status of ayahuasca.

Schenberg interprets the assembled evidence as insufficient to claim that ayahuasca is an effective cancer treatment, but as offering a testable hypothesis with biological plausibility. The authors propose that combined pharmacological actions of DMT and β‑carbolines could affect cancer hallmarks—angiogenesis, apoptosis and altered tumour metabolism—via sigma‑1 receptor modulation, MAO inhibition and direct antiproliferative effects of harmine. They also argue that the powerful psychological effects of ritual use could confer clinically meaningful benefits for anxiety, depression and quality of life in cancer patients, and that these psychosocial dimensions should be integrated into future research designs. Limitations acknowledged include the predominance of anecdotal and heterogeneous case reports, variable and poorly reported doses and compositions of ayahuasca brews, sparse and inconsistent pharmacokinetic data in humans, and conflicting in vitro findings (including possible genotoxicity for some β‑carbolines). The narrative review format and the use of non‑standardised sources (internet reports, books, conference anecdotes) limit the strength of clinical inferences. The authors stress that many important methodological details are missing from the available reports and that underreporting of negative outcomes is possible. For future work, Schenberg recommends systematic collection of clinical cases with detailed objective medical data, controlled preclinical experiments testing individual and combined active principles on relevant cell lines and animal models, and carefully designed clinical research that accounts for set and setting and engages respectfully with indigenous healers. Regulatory, ethical and harm‑reduction issues are discussed: the authors argue that prohibition can worsen set and setting and that careful international regulation might reduce harms associated with unregulated tourism and unsafe practices. Overall, they call for rigorous, multidisciplinary research to evaluate safety and efficacy and to inform potential clinical or policy responses.