There is codeine in prescription Robitussin. Which is what he’s asking for in the tweets.
Actually, the missing component is Robitussin DM, which contains "dextromethorphan". It is common "recreational" drug. It is OTC, no prescription required!.
From a web search:
Dextromethorphan is a common ingredient in cough and cold medicines that acts as a cough suppressant. It manipulates the nerve signals in the part of the brain that controls your cough reflex. While it is not a prescription drug, it can have some dangerous side effects if not used correctly. It is also abused by some in a habit called robo-tripping. In high doses, it depresses the central nervous system and has a similar anesthetic effect to PCP, morphine or the animal tranquilizer ketamine, also known as Special K.
Read more: http://www.ehow.com/list_5796683_effects-dextromethorphan-abuse.html#ixzz2ZNrBCO89