Tetrahydropalmatine (THP) is an alkaloid compound primarily found in the traditional Chinese medicinal herb Corydalis yanhusuo. Historically, THP-containing plants have been used in Traditional Chinese Medicine (TCM) for their sedative, analgesic, and anxiolytic properties. The use of THP for insomnia is rooted in these traditions, where it was believed to "calm the spirit" and promote restful sleep. Over centuries, herbal preparations containing THP have been prescribed to individuals experiencing restlessness, insomnia, and anxiety.

Some preclinical and small-scale clinical studies have investigated THP’s effects on the central nervous system. Research indicates that THP acts as an antagonist at dopamine D2 receptors and may modulate other neurotransmitter systems involved in sleep regulation, such as GABA and serotonin. This pharmacological profile provides a plausible mechanism for its sedative and sleep-promoting effects. However, rigorous, large-scale, placebo-controlled clinical trials in humans are limited. The available scientific evidence is preliminary and does not meet the standards required for strong clinical recommendations.

In summary, the support for using Tetrahydropalmatine for insomnia primarily comes from traditional use and early-stage scientific studies, but robust clinical validation is lacking. Care should be taken due to potential side effects and interactions.