Late 18th century/early 19th century patent medicines, particularly the old English remedies, owed their popularity to the following fact. The multitude of ingredients inside might have varied (unbeknownst to the customer), but the bottle shape did not. A patent medicine’s proprietor believed this distinctiveness leant genuineness to their remedy.
Distinctive packaging may have made patent medicines easily recognizable to even the most illiterate, but it also made them vulnerable to counterfeiters. Naïve proprietors eventually got smart and began to vary their packaging using differing bottle heights, mouth widths, and bottle inscriptions in order to deter counterfeiters. This may also explain why many of today’s products, not just over the counter medicines, change their packaging from time to time. Why chance loosing sales to an unscrupulous competitor?