13 Jun 2011. The half life of Metoprolol is between 3 and 7 hours. This is the time it takes for the drug levels in your plasma to reduce by half. For a drug to be totally eliminated from your system it takes around 5.5 times the half life. As an estimate then, after taking a dose of Metoprolol it should be out of your system within 16.5 to 38.5 hours.