Rationale : The psychedelic effects of the traditional Amazonian botanical decoction known as ayahuasca are attributed to the effects of N,N-dimethyltryptamine (DMT) at brain serotonin 5-HT2A receptors. To make oral DMT bioavailable, ayahuasca additionally contains reversible monoamine oxidase A (MAO-A) inhibitors, namely β-carboline alkaloids such as harmine. However, there is lacking biochemical evidence to substantiate this pharmacokinetic potentiation in the brain. Objectives: Therefore, we measured the pharmacokinetic profile of harmine and DMT in the rat brain. Additionally, we investigated the pharmacodynamic properties of DMT and/or harmine. Methods: We first measured brain concentrations of harmine and DMT after treatment with harmine and/or DMT at low doses (1 mg/kg each) or harmine plus DMT at moderate doses (3 mg/kg each). In the same groups of rats, we also measured ex vivo the effects of these treatments on the availability of serotonin 5-HT2A receptors in frontal cortex. Finally, we explored influences of DMT and/or harmine in the lower dose group on brain glucose metabolism with [18F]FDG-PET. Results: Results confirmed that co-administration of harmine inhibited the formation of the DMT metabolite indole-3-acetic acid (3-IAA) in the brain, while increasing the cerebral availability of DMT. However, we were unable to detect any significant occupancy by DMT at 5-HT2A receptors measured ex vivo, despite brain DMT concentrations as high as 11.3 µM at moderate doses. We did not observe strong influences of low dose DMT and/or harmine on [18F]FDG-PET. Conclusions: The present preliminary results call for further experiments to establish the dose-dependent effects of harmine/DMT on receptor occupancy and on cerebral metabolism.