Then (1993), True Hallucinations
The Endogenous DMT Confirmation: Is the Spirit Molecule Really There?
Strassman's hypothesis, that the pineal gland produces elevated DMT at key life transitions, was circulating in the psychedelic community before True Hallucinations was published. McKenna was aware of it and incorporated it into his worldview. Both McKenna and Strassman believed that endogenous DMT was a key to consciousness, dreaming, and near-death experience.
partially-confirmed
Barker, McIlhenny and Strassman (Drug Testing and Analysis, 2012): reviewed reports of DMT in human blood, urine and cerebrospinal fluid, with inconsistent methods across studies. The enzymes for DMT synthesis (INMT, AADC) are present in the brain, lung, and other tissues. Dean et al. (Scientific Reports, 2019): measured DMT in rat brain and found levels in the visual cortex rose after experimental cardiac arrest; this is a rat finding and does not test the near-death experience hypothesis in people. The pineal gland-specific hypothesis: the pineal has the enzymatic machinery but no study has demonstrated that it produces elevated DMT at near-death, during sleep, or at birth in concentrations sufficient for psychedelic effect. Endogenous DMT exists. Its biological role remains unclear. Strassman's specific pineal-at-key-moments hypothesis is unconfirmed.