elixir
An elixir is a clear, sweet oral liquid that has a splash of alcohol in it. Think of it as a syrup's lighter, see-through cousin: less syrupy and thinner because part of the water has been swapped for ethanol, which helps dissolve drugs that plain water cannot.
Technically an elixir is a sweetened hydroalcoholic (water-plus-ethanol) solution. The ethanol acts as a cosolvent, raising the solubility of drugs that are weakly water-soluble or that carry oily aromatic flavouring oils, and it keeps the product clear. Glycerol and propylene glycol are often added as additional cosolvents and to give body, since elixirs lack the high sugar content of syrups.
The alcohol content is the catch. Because ethanol can range from a few percent up to 20% or more, elixirs are generally unsuitable for young children, for patients avoiding alcohol, and for drugs that might precipitate when the alcohol is diluted in the stomach. The same cosolvent that dissolves the drug can cause it to crash out of solution if the formula is later watered down.
Phenobarbital elixir uses ethanol and propylene glycol as cosolvents to dissolve the poorly water-soluble drug while staying clear and palatable.
Adding alcohol as a cosolvent dissolves a drug that water alone cannot.
An elixir is a true solution, so it must stay clear; if a drug needs alcohol only to dissolve and would precipitate on dilution, a different dosage form is safer.