If you take beta-blockers , ask your doctor how many bananas you can consume because of the potassium in the bananas. Beta-blockers raise potassium in the blood, which is fine. But too much potassium may be harmful to the kidneys.
Some people are allergic , so avoid them if you experience hives, difficulty breathing, etc.
Some people say bananas cause migraines. Talk to your doctor about this if you experience migraines.