While less common, the most serious side effects of psilocybin are described below, along with what to do if they happen. Severe Allergic Reactions. Psilocybin may cause allergic reactions, which can be serious. Stop taking psilocybin and get help right away if you have any of the following symptoms of a serious allergic reaction. Breathing problems or wheezing Racing heart Fever or general ill feeling Swollen lymph nodes Swelling of the face, lips, mouth, tongue, or throat Trouble swallowing or throat tightness Itching or skin rash Bumps on the skin called hives that can be red, pink, white, or brown depending on your skin tone Nausea or vomiting Dizziness, feeling lightheaded, or fainting Stomach cramps Joint pain Hallucinations. Psilocybin can cause hallucinations that may involve hearing, seeing, smelling, tasting, or otherwise perceiving things that others do not. These hallucinations are often part of the reason that people take psilocybin. But some hallucinations can cause a negative experience during a psychedelic trip. Taking psilocybin in a safe setting with a trained professional who can monitor you may help reduce the risk of negative hallucinations. Psychotic-like Behaviors. Psilocybin may cause psychotic-like behaviors. This risk may be higher in people who have a negative experience while taking psilocybin. Taking psilocybin in a safe setting with a trained professional who can monitor you may help reduce this risk. Tell your health care provider right away if you have any of the following symptoms or if you have been told by others that you have these symptoms. Delusional thoughts, such as false beliefs that you are being controlled Disorganized thoughts, such as jumping between topics or having a hard time focusing Sudden decline in self-care, such as personal hygiene or academic/work performance Aggressive behavior Dangerous Behavior. Psilocybin has psychedelic effects, which can cause hallucinations and change the way that you experience the world around you. This may increase your risk of doing things that can be dangerous to you or others, such as walking into traffic or off of a tall ledge. To help reduce your risk of dangerous behavior, psilocybin should be taken in a safe setting with a trained professional who can monitor your health and safety. Suicidal Thoughts or Actions. Psilocybin may increase the risk of suicidal thoughts or actions in some people. The risk is higher in people who had a negative experience while taking psilocybin. Taking psilocybin in a safe setting with a trained professional who can monitor you may help to reduce this risk. If you or someone you know is about to harm themselves, call 911 or call or text 988, the Suicide & Crisis Lifeline. Tell your health care provider right away if you have any of the following symptoms. New or increased thoughts of suicide or death Suicide attempt New or increased feelings of anxiety, depression, or other unusual changes in your mood or behavior Warnings & Precautions Who should not use psilocybin? Allergies to Ingredients. People who are allergic to any of the following should not take psilocybin. Psilocybin Any of the ingredients in the specific product What should I know about psilocybin before using it? The U.S. federal government does not consider psilocybin to be a legal ingredient. It is a Schedule I controlled substance, which means that it does not have any approved medical uses and is at high risk for misuse. Some U.S. states have laws that allow the use of psilocybin in certain cases, such as in approved treatment facilities. Psilocybin and magic mushrooms are not regulated and have not been tested to confirm that they contain the claimed ingredients. Psilocybin is a controlled substance because it can be misused. If you will store psilocybin at home, keep it out of the reach of children and store it in a safe place. Different doses of psilocybin can have very different effects on the brain. A psychedelic dose of psilocybin can produce a psychedelic trip, which involves hallucinations. Microdoses do not usually cause hallucinations because they are less than one-tenth of a psychedelic dose. But all doses of psilocybin can affect the brain and cause side effects. Psilocybin can affect your alertness or coordination. If you are using a full psychedelic dose of psilocybin, do not drive or do other activities that require alertness or coordination until the next day. If you are taking microdoses of psilocybin, you should not do these activities until you know how psilocybin affects you. Do not confuse psilocybin with magic mushrooms, which contain psilocybin. Psilocybin is removed from magic mushrooms or made in a lab so that it can be given in controlled doses. Mushrooms, on the other hand, naturally contain many chemicals in addition to psilocybin. The amount of each chemical in a specific batch of mushrooms can change for many reasons, including how the mushrooms were grown and the way that they were processed. Switching between batches of mushrooms can change the effects and side effects. Raw, dried, cooked, or powdered mushrooms may each have different effects on the body. What should I tell my health care provider before using psilocybin? Tell your health care provider about all of your health conditions and any prescription or over-the-counter (OTC) medicines, vitamins/minerals, herbal products, and other supplements you are using. This will help them know if psilocybin is right for you. In particular, make sure that you discuss any of the following. Current and Past Health Conditions. Tell your health care provider if you have any of the following. Heart problems Mental health problems, such as depression, a past suicide attempt, anxiety, hallucinations, paranoia, or psychosis History of misusing prescription medicines or street drugs Drink large amounts of alcohol Other Medicines and Supplements. Psilocybin may interact with other medicines and supplements. Before taking psilocybin, tell your health care provider about any prescription or over-the-counter (OTC) medicines, vitamins/minerals, herbal products, and other supplements you are using. See the Interactions section for more details. Pregnancy. It is not known if or how psilocybin could affect pregnancy or harm a fetus. Tell your health care provider if you are pregnant or plan to become pregnant. Breastfeeding. It is not known if psilocybin passes into breast milk. Tell your health care provider if you are breastfeeding or plan to breastfeed. Explore More On Mental Health Sexual Problems in Men Written by Kathleen Fordyce. Medically reviewed by Jennifer Casarella on December 17, 2022 Many men have problems during sex, ranging from lack of desire to erection issues. Learn more about what causes male sexual problems and what you can do about them.