Metoprolol starts to work within about 1 hour after taking oral tablets, with effects on heart rate and blood pressure often noticeable at that time. The injectable form works faster, showing effects within about 20 minutes. However, it may take 1 to 2 weeks of consistent use to see the full benefits, especially for conditions like high blood pressure. Dosages and how quickly the medication works depend on the specific form (immediate-release or extended-release) and the condition being treated.