I have absolutely no idea as to how Levomepromazine elicits its analgesic effects so please do direct me to journal articles and other credible sources with you, the answerer, making a summary of Levomepromazine's mechanism of action in your answer.
According to Drugbank and the articles cited below, Levomepromazine is an antagonist of several different receptors: These include dopaminergic 2, dopaminergic 4, alpha-1 adrenoceptor, 5HT-2, histamine type 1 and muscarinic-cholinergic receptors.
- Evidence for the use of Levomepromazine for symptom control in the palliative care setting: a systematic review
- Muscarinic cholinergic and histamine H1 receptor binding of phenothiazine drug metabolites
- Levomepromazine receptor binding profile in human brain—implications for treatment—resistant schizophrenia
- Phenothiazine drug metabolites: Dopamine D2 receptor, α1-and α2-adrenoceptor binding