Metoprolol starts to work within about 1 hour after oral intake for its heart rate-lowering effects, and within 20 minutes if given intravenously. However, the full effects of metoprolol, particularly for conditions like high blood pressure or heart failure, can take about a week or more to be fully noticed. The immediate-release form (metoprolol tartrate) works faster within an hour, while the extended-release form (metoprolol succinate) releases the medication gradually and also begins working within about an hour but provides longer- lasting effects. Dosage adjustments over weeks may be needed to reach the optimal effect depending on the condition being treated.