Comment by PaulDavisThe1st

If your resting heart rate is lower without any drugs, it indicates that your heart can cause sufficient oxygen to be delivered to your organs with less effort than if it were higher. That can be caused by a variety of things (including stroke volume, capillary dilation and general obstruction (or not) of blood vessels). These are all good proxies for general health.

Drugs lowering your resting heart rate do not indicate this in the same way.