Brief Summary:

Background: Major Depressive Disorder is one of the most prevalent mental illnesses, leading to substantial personal distress and economical consequences. Pharmacological Treatment is limited and relapse is frequent.

Lysergic acid diethylamide (LSD) was extensively investigated in humans in the 1950s and 1960s and was shown to attenuate depressive symptoms. Clinical research with LSD ended in the 1970s due to regulatory restrictions but its use for personal and recreational purposes continued. In recent years, there has been a renewed interest in the use of hallucinogens in psychiatric research and practices, reconsidering LSD's antidepressant potential. Larger, well-designed and placebo-controlled studies are warranted. This study will evaluate the potential benefits of LSD-assisted psychotherapy in patients suffering from Major Depressive Disorder.

Objective: To test the efficacy of LSD in patients with Major Depressive Disorder.

Design: Randomised, double-blind, active-placebo-controlled trial using either two moderate to high doses of LSD (100 µg and 100 µg or 100 µg and 200 µg) as intervention and two low doses of LSD (25 µg and 25 µg) as active-placebo control.

Participants: 60 patients aged > 25 years with Major Depressive Disorder (according to DSM-V).

Main outcome measures: Change in depressive symptomatology (IDS-SR, BDI), anxiety (STAI), and general psychopathology (SCL-90) compared with active-placebo-assisted psychotherapy.