This Phase I, randomised, triple-blind trial (n=80) will assess the safety, feasibility, and mechanisms of psilocybin and dextromethorphan in healthy older adults aged 50 to 90 years with low well-being. The study aims to evaluate whether psilocybin can acutely increase the complexity of EEG activity and longitudinally decrease plasma markers of neuroinflammation, while also exploring changes in autonomic physiology and brain structure and function over time. Participants will be assigned to one of four experimental arms, receiving either a low-to-moderate (5-10 mg) or moderate-to-high (25-30 mg) dose of psilocybin, or a low-to-moderate (30-60 mg) or moderate-to-high (80-90 mg) dose of dextromethorphan. The trial will involve up to 3 months of participation, including 3 to 4 in-person visits and 3 to 4 remote visits, with the dosing visit lasting between 8 to 12 hours. Primary outcomes will focus on acute changes in EEG-based measures two hours post-dose.
This study is being conducted to understand changes in brain activity following administration of two different drugs (Psilocybin and Dextromethorphan) in older adults with low well-being.
The main questions it aims to answer are, does psilocybin:
1. Acutely increase complexity of EEG activity in older adults with low well-being, as modulated by the presence of biomarkers of Alzheimer's disease (AD) pathology.
2. Longitudinally decrease plasma markers of neuroinflammation, as modulated by the presence of biomarkers of AD pathology.
3. Explore longitudinal changes in autonomic physiology via wearable recording devices as well as longitudinal structural and functional brain changes measured in the MRI
Participants will be in the study for up to 3 months, which will include 3 to 4 in person visits and 3 to 4 remote visits. Most visits will be between 1 to 3 hours, but the dosing visit will last a minimum of 8 hours and could be as long as 12 hours. During the dosing visit, all participants will receive a single dose of the study drugs and dosages listed below.
Researchers will compare participants who receive the following drug options:
* A low-to-moderate dose of Psilocybin (5-10 mg)
* A moderate-to-high dose of Psilocybin (25-30 mg)
* A low-to-moderate dose of Dextromethorphan (30-60 mg)
* A moderate-to-high dose of Dextromethorphan (80-90 mg)
A single low-to-moderate dose of Psilocybin (5-10 mg)
A single moderate-to-high dose of Psilocybin (25-30 mg)
A single low-to-moderate dose of Dextromethorphan (30-60 mg)
Unmatched intervention: Dextromethorphan (DXM)
A single moderate-to-high dose of Dextromethorphan (80-90 mg)
Unmatched intervention: Dextromethorphan (DXM)