Short answer: In a controlled setting with healthy volunteers, short-term escitalopram pretreatment appeared to reduce psilocybin’s negative effects (like anxiety and other adverse effects) without meaningfully reducing the positive subjective effects of a 25 mg dose (study).
Escitalopram did not change psilocin pharmacokinetics, and there were no observed changes in QTc intervals or circulating BDNF levels. This points to a pharmacodynamic interaction rather than less active drug in the blood.
Important caveats: the data come from healthy participants after only 14 days of escitalopram. It does not establish what happens with long-term antidepressant use or in clinical populations. More research is needed before drawing broader conclusions.
Hope this clarifies what the study found.