In Only Lovers Left Alive, it's clear that blood is in limited supply. Adam and Eve both comment that they've got "the good stuff" and discuss a "contamination" that appears to have infected the human population. Ava seems desperate for blood when she visits, and Adam repeatedly tries to stop her from drinking as much as she does.
Despite their superhuman speed and longevity, and Eve's ability to tell how old something is by touching it, the vampires don't seem to exhibit any other supernatural abilities. In particular, they do not have superhuman strength:
When Eve and Adam dump the body in the river, they must work together to lift and toss it.
They also seem quite lethargic, especially near the end of the film when
they arrive in Tangiers and cannot find a source of uncontaminated blood.
In Adam's case, the lethargy could merely be due to his depression, and indeed Eve seems somewhat less lethargic than he does.
Did Jim Jarmusch (the writer and director) intend the vampire's lethargy and/or their lack of superhuman strength to be an effect of their limited blood supply? Or do vampires in this world simply lack supernatural strength and act lethargic?