Propranolol is contraindicated in diabetes mellitus because it
Causes hyperglycemia
uses seizures
Masks the hypoglycemic symptoms
Causes hypotension
Ref; KD Tripathi pharmacology 7th edition (page no; 146) Propranolol delays recovery from hypoglycemia due to insulin and oral antidiabetics. It masks the warning signs of hypoglycaemia mediated through sympathetic stimulation (tachycardia, tremor).
Autonomic nervous system