Cialis dilates small blood vessels all over the body. This tightens back muscles just enough to sometimes cause lower back ache.
If you switch to low dose daily, after a few weeks of a steady blood level of tadalafil, your vascular system will compensate by constricting some of the small blood vessels again and the discomfort will go away, along with any other sides you get using "on demand" cialis.
The good news is the pump and other "benefits" of Cialis will be just as good on 2.5 or 5mg daily as they are on 10 or 20mg on demand.
It's also been demonstrated to be good for cardiovascular and brain health, and safe even after decades of daily use. If you buy it right, should only cost around $5 a month.