How long it takes metoprolol to work depends on what form is given and what condition is being treated. Effects on heart rate can be seen within one hour after taking metoprolol tartrate tablets and within 20 minutes after the intravenous form is given. The onset of action of metoprolol succinate is similar to metoprolol tartrate.

Metoprolol tartrate is immediate release (fast-acting), while metoprolol succinate is extended release (released over time). You usually take metoprolol tartrate twice daily and take metoprolol succinate once daily. Metoprolol tartrate also comes as an injection that’s given in the hospital and used in the early stages of a heart attack.

The dosage of metoprolol may need to be adjusted depending on what condition is being treated.

• For high blood pressure or angina, the dosage may be increased at weekly intervals to reach the maximum effect.
• For heart failure, the dosage of metoprolol succinate may be doubled every 2 weeks to reach the maximum effect.
• For heart attacks that are caught early, the intravenous form of metoprolol tartrate is usually given. If treatment is started later, metoprolol tartrate tablets are usually given twice daily.