Some spices are known for temporarily increasing thermogenesis, heat production, which causes a slight rise in metabolic rate. But I would not count on this as a weight loss strategy just yet. The increase in metabolism is very small and there is little to no research in humans to show that adding more black pepper to you meals has metabolic benefits for calorie burning.
A study with mice did find that the mice that ate black pepper or piperine (compound found in black pepper) did increase body heat or thermogenesis which means an increase in basal metabolism. These mice had a decrease in body weight and abdominal fat. Piperine may work by helping to prevent fat from being stored. This study was published in Bioscience, Biotechnology, and Biochemistry in October 2010.
Even if it does change metabolism much, pouring on the pepper could be beneficial in other ways. The component piperine, may do other healthful things for us like help lower blood pressure and prevent oxidative stress that can damage arteries. There does not seem to be any harm in adding a bit more pepper to your foods and it is a good way to add flavor without adding salt, fat, or more calories. Feel free to sprinkle it on.