How is imipramine pamoate (Tofranil-PM®) different from imipramine hydrochloride (Tofranil®)?

Question from a Member: A question about imipramine hydrochloride versus imipramine pamoate. The pamoate is much more expensive than hydrochloride but the pamoate says that it’s “PM” as in “Tofranil-PM”, while the hydrochloride is just “Tofranil”. Is the pamoate actually more sedating, or is this some sort of marketing thing? Among the tricyclic antidepressants, the…