Lean is thought to have developed in Houston around the 1960s, when blues musicians would take Robitussin and cut it with beer. Later, when wine coolers came onto the market, they substituted for beer.
The practice of mixing Robitussin with alcohol, known as "lean," emerged in Houston during the 1960s. When wine coolers were introduced to the market, they took the place of beer as a common ingredient for this concoction.