Many salt substitutes contain potassium in place of all or some of the sodium. For some people, potassium consumed in excess can be harmful. For example, those with kidney problems may not be able to rid their bodies of excess levels of potassium.
Rather than salt substitutes, try herb-spice blends as a flavorful alternative to salt, or lemon or lime juice. Today's supermarkets carry a variety of salt-free seasoning blends. Remember to read the ingredient list and the Nutrition Facts on the label, since some herb-spice blends are neither salt- nor sodium-free.