You have been taking Tenolol-50 (atenolol), a beta-blocker, for 15 years, which shows it has been working well for you. Long-term use is generally safe, but some patients may experience mild side effects like fatigue, cold extremities, slow heart rate, or sleep changes over time. The best solution is regular monitoring by your doctor, including routine checks of your blood pressure, heart rate, and kidney function. If you ever feel these side effects are bothersome, your doctor can safely adjust your dosage. Please do not stop taking this medication abruptly, as a gradual taper is necessary to keep your heart safe.