Atenolol is a beta blocker, but its half-life is far longer than what is the case with <span style = 'background-color: #dae8f4'>metoprolol</span>
(6-9 hours <span style = 'background-color: #dae8f4'>vs</span>
3-4 hours). So extended release is not quite as necessary.
Some beta blockers are able to cross the blood-brain barrier and some are not. propranolol
are fairly able to do so, but Atenolol is, as far as I know, not. Which means, propranolol
can provide more cognitive side effects (forgetfullness, confusion, mood disturbances, etc.) than Atenolol.