The answer to this question depends on a number of factors. For one, the type of workout you are doing. If your workout is heavy strength training, then your body will need more time to recover from the damage caused by those exercises. On top of that, the intensity and frequency of your workouts also affect how long a pre-workout will work for you. In general, if you are working out intensely and often, then you can expect your pre-workout to last for about 3 hours after ingestion. However, if you are only working out once or twice a week and not too intensely, then it might last for up to 8 hours.