Some drugs require a salt to be added to them to ensure that they can dissolve in the stomach or be absorbed into the bloodstream. Sometimes salts make medicine more stable so that it has a longer shelf life. More than 50% of all available medicines exist as salts.

Hydrochloride is the most commonly used salt, and 15.5% of all drugs contain it. All types of oxycodone are the hydrochloride salt, but sometimes drug data information will just shorten the name to oxycodone. But oxycodone hydrochloride and oxycodone are the same medicine. There are some medicines, for example metoprolol, that have two different salts (in this example metoprolol tartrate and metoprolol succinate). If a medicine has two different salts these are usually not interchangeable.

Other common salts include:

• sodium (9%)
• sulfate (4%)
• acetate (2.5%)
• phosphate or diphosphate (1.9%)
• chloride (1.8%)
• potassium (1.6%)
• maleate (1.4%).

The choice of salt primarily comes down to the pH of the medicine (this is how acidic or alkaline it is). Other factors that affect salt choice include the natural stability of the medicine, its intended use, how it is going to be administered (such as by mouth, by injection, or applied on the skin) and the intended dosage form (such as a tablet, capsule, or liquid).

Salts may also be added during the manufacture of a controlled-release form, to improve a medicine's taste, its effectiveness, to make it less painful if it is going to be injected or to extend the patent life.

For more information see Drug Names and Their Pharmaceutical Salts - Clearing Up the Confusion.