Hello, There can be various reasons for irritability in your dad and stamlo beta can cause this irritability especially if it has been started recently. In fact both the drugs( AMLODIPINE and atenolol ) present in stamlo beta can result in sleep disturbance,depression and headache. In fact your dad should be put on ACE inhibitors or ARB s instead of stamlo beta since he is diabetic and hypertensive. Other reasons for irritability could be uncontrolled diabetes and blood pressure,sleep disturbance,depression,use of alcohol or other drugs and even their withdrawl,if he is addicted to them,some other medical condition like thyroid problems,neurological problems like ALZHEIMER s or some brain pathology. What you require is a visit to your doctor for proper check up and treatment and if required,may be a visit to neurologist or a psychiatrist. Thanks