Dave's retarded because I've never seen him actually be correct with respect to any subject he's discussed that I've seen shared here.
Clen is a β2 agonist (analogous to terbutaline) & nebivolol is a selective β1 antagonist. See:
The beta1-selectivity of three different beta1-blockers has been demonstrated in healthy volunteers using the blocking of biochemical and haemodynamic responses to a beta2 stimulus. Terbutaline alone caused an increase in heart rate, a rise in systolic blood pressure, a fall in serum potassium...
pubmed.ncbi.nlm.nih.gov
"The beta1-selectivity of three different beta1-blockers has been demonstrated in healthy volunteers using the blocking of biochemical and haemodynamic responses to a beta2 stimulus. Terbutaline alone caused an increase in heart rate, a rise in systolic blood pressure, a fall in serum potassium and a rise in both serum glucose and insulin. In this study, for both haemodynamic and biochemical responses, atenolol 100 mg had the greatest beta2-blocking effect,
nebivolol 5 mg the least. Bisoprolol 10 mg and atenolol 50 mg had intermediate effects; bisoprolol was the more beta1-selective of these two."