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.