Which of the following is a common side effect of cocaine use?

The option identifying "Rat nose" as a side effect of cocaine use pertains to the physical appearance changes that can occur due to prolonged cocaine use. Users of cocaine may experience alterations in their facial features, particularly around the nose, due to the constricting effects of cocaine on blood vessels, leading to issues like decreased blood flow and tissue damage. This effect is informally referred to as "coke nose" or "rat nose" and is a direct result of the drug's impact on nasal tissues, including chronic irritation and ulceration.

The other options suggest effects that either do not typically occur with cocaine use or are misleading regarding the substance's action. While increased metabolism can describe some stimulant effects, it is not as consequential or characteristic as the changes observed in nasal regions from cocaine use. Improved cognitive function is unlikely, as cocaine typically impairs cognitive and motor functions in the long term. Muscle relaxation is generally not associated with cocaine, which is a stimulant causing increased energy and tension rather than relaxation.