Psilocybin mushrooms, commonly called “shrooms,” contain the psychoactive compound psilocybin. Psilocybin is rapidly converted in the body to its active form, psilocin, which acts as a non-selective agonist on serotonin receptors in the brain, primarily the 5-HT2A receptor. The substance is classified as a hallucinogen and is a Schedule I controlled substance in the United States, meaning it currently has no accepted medical use and a high potential for misuse. Psilocybin use is strongly advised against during pregnancy due to a significant lack of safety data and unknown risks to the developing fetus.
Why Human Safety Data Is Absent
Controlled human studies on psilocybin use during pregnancy are considered unethical, which explains the complete absence of clinical trial data regarding fetal safety. The developing fetus is highly vulnerable to external chemical exposure, and researchers cannot knowingly expose a pregnant individual and their child to an unproven risk. Psilocybin’s molecular properties—small size and lipid solubility—strongly suggest that both the prodrug psilocybin and its active metabolite psilocin can cross the placental barrier. This means the compound would reach the fetal bloodstream and brain.
The primary concern involves the fetal neurobiological risk due to psilocin’s action on serotonin receptors. Serotonin is a fundamental signaling molecule that plays a crucial role in regulating the formation and wiring of the central nervous system during development. Disrupting this system with a powerful 5-HT2A receptor agonist during critical periods of fetal brain growth raises the potential for teratogenicity or long-term neurodevelopmental alteration. Early disruption of neural pathways could lead to permanent changes in brain structure and function.
One animal study in rats showed that psilocybin crossed the placental barrier and accumulated in fetal tissue, confirming the theoretical mechanism of exposure. While this study did not assess developmental issues, another animal study showed no increased chance of birth defects, demonstrating the complexity and uncertainty of the substance’s effect. Without human evidence, the potential for altering the delicate process of neurodevelopment remains the most significant, though unquantified, risk.
Acute Maternal Physiological Concerns
The psychedelic experience itself presents immediate, indirect dangers to the fetus through maternal physiological changes. Psilocybin is known to cause sympathomimetic effects, meaning it stimulates the sympathetic nervous system. This typically results in a transient, dose-dependent increase in both heart rate and blood pressure in the person taking the substance.
During pregnancy, these acute cardiovascular changes are a significant concern because they can compromise blood flow to the placenta. Increased maternal blood pressure or vasoconstriction (the narrowing of blood vessels) can reduce the delivery of oxygen and nutrients to the fetus. A sudden spike in maternal blood pressure could potentially place the fetus under acute stress, especially if the person has an underlying cardiovascular condition.
Furthermore, psilocybin can induce intense psychological states, including acute panic, extreme anxiety, or even a temporary state of psychosis, commonly known as a “bad trip”. This extreme maternal stress response releases a cascade of stress hormones, which can cross the placenta and potentially influence fetal development and stress regulation. The emotional intensity of a psychedelic experience, combined with the physical strain of elevated heart rate and blood pressure, creates a situation where the pregnant individual’s body is under significant duress.
Postpartum and Nursing Considerations
Following childbirth, psilocybin use continues to carry risks, particularly for the nursing infant. Psilocybin and its active metabolite, psilocin, are small, lipid-soluble molecules, a characteristic that allows substances to transfer from the mother’s bloodstream into breast milk. Although no high-quality studies have measured psilocybin or psilocin concentration in human breast milk, experts predict infant exposure is likely.
The full effect of these compounds on a newborn’s developing brain is unknown, but exposure to a psychoactive substance that interacts with serotonin receptors is the primary concern. The recommendation is to avoid psilocybin use entirely while nursing to prevent substance transfer to the infant. For individuals who do use psilocybin, the active compound psilocin is largely eliminated quickly, with some experts suggesting a wait time of 24 to 48 hours before resuming breastfeeding to minimize potential exposure.
Beyond the physiological transfer, the vulnerable postpartum period presents unique risks regarding maternal mental health and infant bonding. While some research is exploring psychedelics for conditions like postpartum depression, a recent animal study in mice suggested that psilocybin amplified anxiety and depressive-like symptoms in mothers. Using a potent psychoactive substance during this time could interfere with the critical process of mother-infant bonding or potentially exacerbate existing postpartum mood disorders, rather than alleviate them.