It is probably one of the most frequently asked questions you can find on almost every health forum. Most people want to know exactly How Long Does thc Stay in Blood so that they can successfully pass a drug test. There a few methods of testing for weed levels, and blood tests are the most common, especially when driving under the influence of drugs is suspected. The amount of time that THC stays in your blood depends on lifestyle factors, including how, how often, and what kind of strain the user consumed, as well as his body's rate of metabolism. For successfully passing a marijuana drug test, it is important to understand what THC exactly is and how it works in our bodies.