The Government of Antioquia (the departamento where Medellin is located) produces two different types of liquor: Ron Medellín, and Aguardiente. Ron is simply rum, in English, and the most common variety is a dark rum aged three years. Aguardiente, often referred to as Guaro by the locals, is a licorish-flavored alcohol.
All other liquor is subject to fairly sizeable import taxes, which makes bottles of anything besides these two alcohols noticeably more expensive. Because of this, these two types of alcohol tend to be consumed at a disproportionately high rate on a normal night out.
While some might see this as a protectionist policy that discourages outside investment, it is worth noting that the proceeds of alcohol sales by the Provincial Government (officially distributed by La Fabrica de Licores de Antioquia) are used to fund the public school systems in the region. If they are drinking heavily on a night out, my Colombian friends will often joke that they are doing so… para que los niños puedan aprender! (so that the children can learn)