Sodium picosulfate works by encouraging the muscles in your bowel to move waste products through your body. This helps you to go to the toilet. It usually has an effect within 6-12 hours. Sodium picosulfate preparations are available to buy without a prescription at pharmacies and other retail outlets. Preparations containing sodium picosulfate (in combination with another laxative called magnesium citrate) are sometimes used to clear the bowel before some medical examinations. When it is used like this, you will be provided with sachets of powder by your hospital or clinic. You will also be given full instructions for how to use them.