It isn’t safe to suddenly stop taking Lopressor without first telling your doctor. Suddenly stopping Lopressor can cause serious heart problems, including:
heart attack
worsened chest pain
life threatening changes in your heart rhythm
Suddenly stopping Lopressor can also cause a condition called thyroid storm in people who have hyperthyroidism. (With hyperthyroidism, you have an overactive thyroid gland.)
If your doctor recommends that you stop taking Lopressor, they will probably gradually lower your dosage of the drug over a couple of weeks. They will also monitor you closely for worsening heart problems.