Final answer:
The combination of simvastatin and niacin can lead to rhabdomyolysis, a severe form of myopathy characterized by the breakdown of muscle tissue.
Step-by-step explanation:
The complication that can occur when a patient is taking simvastatin (Zocor) and niacin is C. Rhabdomyolysis. This is due to the increased risk of myopathy when these drugs are used in combination. Rhabdomyolysis is a severe form of myopathy that involves the breakdown of muscle tissue leading to the release of muscle fiber contents into the bloodstream. This can result in severe kidney damage. While both simvastatin and niacin individually can cause myopathy, their combination can markedly increase this risk, which is why such combination therapy is only done under close medical supervision.