A compounding pharmacy is able to create a customized medication for you. Your doctor can order almost any medication at any strength, various types of administration (cream, capsule, dissolvable tablet, liquid, etc.) and use various fillers/vehicles.
We commonly use a compounding pharmacy to create low dose naltrexone. Naltrexone is commercially available at 50mg, but we often start our patients at 0.1mg. Therefore, a compounding pharmacy can create pills of 0.1mg of Naltrexone, and dispense these pills to our patients so we know that they are taking the correct amount.
Compounding pharmacies go through rigorous testing to make sure they are creating the correct dosage of medication in a sterile setting.