Methocarbamol (Robaxin) has a very short half life of 1-2 hours. It is unlikely to show up in a blood test to screen for drug use, unless you take it near the time of the actual blood draw for your blood work. If you are concerned about methocarbamol showing up in a drug screen, you can discontinue it several days prior to the test. Also, you can inform the person requesting your blood test about your prescription and usage before you have the blood work done. A legal prescription for the methocabamol will help to explain why you might test positive for methocarbamol if the blood test is screening for this.