Prepare for your Driver's Tiredness Blood Test by following these instructions. Please take your sample before 10am. Take this test when any symptoms of short-term illness have settled. You should take this test before you take any medication or vitamin/mineral supplements. Do not take biotin supplements for two days before this test, discuss this with your doctor if it is prescribed. Do not take vitamin B12 for two weeks prior to this test. If your B12 is prescribed ask your doctor whether to stop.