Keep in mind that when you switched from Toprolol ER (
Metoprolol Succinate) to Lopressor (
Metoprolol Tartrate), you lost the timed released advantage. If you were taking 25mg. pills of each medication, you are loosing a great deal of the latter drug's effectiveness as the day wears on. The half life of Metoprolol Tartrate is only 3-7 hours. So you must take it at least twice a day for it to be effective the entire 24 hour period. Also 25mg., once a day is a a very small dose.