In this triple blind (patient, therapist, independent evaluator) RCT, 40 patients with PTSD receiving standard Cognitive Processing Therapy will be randomized in a 1:1 ratio to receive either odorless Hexadecanal molecules or odorless mineral oil molecules (Control) diffused in the treatment room at all therapy sessions. Inclusion criteria: age\>18 years, PTSD diagnosis according to DSM-5-TR. Exclusion: Bipolar, psychotic, or neurological disorders, drug abuse, any parallel psychotherapy, anosmia. Primary outcome: pre-to-post treatment change in PTSD symptom severity measured by the PTSD check List for DSM-5 (PCL-5). Additional outcomes: Depression (PHQ-9), anxiety (GAD-7), Anger (DAR-5), therapeutic alliance (WAI-SF).
