Your repeat prescription lists all the things you have on repeat - each item has a box next to it - if you need an item, put a tick in the box, if you don't, don't tick the box. They will issue the item you have asked for and give you back your repeat prescription, which will continue to have all of the same items on it. Most of the items we have (needles, test strips, insulin) will be prescribed "as needed" so there is no set time frame on when you can reorder. However, each script will need to be signed off by your GP (or more likely their prescribing clerk/admin) and if it looks like you are ordering "too much" of something, they might not sign off before they have actually seen & discussed with you.