It depends upon the quantity and form of the valium and age of the patient taking it. If you take the oral form, it stays in your system for 2 to 3 hours. If you take it rarely or once, it’s not detectable after a few days. If taken intravenously, the peak effect of the drug happens two hours after taking it, and the drug can stay in your body for 14 days. If it is taken for a longer time or there is chronic usage of it, it can be detected for up to 30 days.