Abigail Calder

PhD Candidate, University of Fribourg

The bad and the ugly: Understanding negative effects from psychedelics


For decades, most rhetoric about psychedelics focused on their negative effects. This might make it seem like we know all there is to know about bad reactions to psychedelics - but how much do we really know? In this talk, I aim to separate fact from fiction and give an update on the unwanted, negative effects that can occur with psychedelics, in all settings. 

I start by outlining the range of possible negative effects, from brief delusions to longer-lasting psychological difficulties. Next, I will discuss the prevalence of the most concerning negative effects using new data from two different studies, as well as what puts people at greater risk of these outcomes. On the way, I will touch on some special topics that don’t get much attention, including the prevalence of true hallucinations on psychedelics, the role of people’s beliefs about psychedelics, and whether some psychedelics are more prone to causing problems than others. Despite the gloomy subject, I hope to end on an optimistic note and leave you with an idea of how researchers, clinicians, and everyone else involved with this young field can help prevent and cope with the reality of adverse reactions to psychedelics in the future.


Abigail Calder is a PhD candidate at the University in Fribourg, Switzerland, where she heads a research project on the effects of LSD on neuroplasticity in healthy people. She also conducts research into the adverse effects of psychedelics and their underlying causes, as well as psychedelics’ effects on people’s values and well-being, and she recently joined the ALPS Foundation as its research coordinator. She completed her Master’s degree in neuroscience at the University of Bonn and holds a Bachelor’s in psychology from TU Dresden.