It can be argued that the success of Postum was largely due to the ridiculous claims made by Post and his many shills, who posed as medical experts and blamed coffee for practically every malady imaginable. Gullible consumers were frightened into believing that coffee caused problems such as "... divorces, business failures, factory accidents, juvenile delinquency, traffic accidents, fire or home foreclosures ... ", as well as a vague condition called "coffee heart". Postum was touted not only as a healthy alternative to evil coffee, but was also sold as a cure to appendicitis, among other things. These claims were plastered in countless advertisements and were reinforced by tracts such as Post's 12-page booklet, "The Road To Wellville", which the company included in boxes of Grape-Nuts cereal. Despite the Post Cereal Company's meteoric growth in the first half of the 20th century, they clung to many of their most outrageous medical claims until the FTC intervened in 1951.

Even with loyal Postum consumers eventually dying off every year, the product managed to survive into the 21st century as a staple of the Mormons, Seventh-Day Adventists, and other fervent anti-caffeine groups. In late 2007, Kraft Foods decided to stop making Postum entirely, citing insufficient consumer demand.