Complex sentence: No long-term studies have been done on the effectiveness of e-cigarettes in treating tobacco addiction, but some evidence suggests that dual use of e-cigarettes and traditional cigarettes may be associated with greater nicotine dependence.
Split into simpler sentences: No long-term studies have been done on the effectiveness of e-cigarettes in treating tobacco addiction. Some evidence suggests that dual use of e-cigarettes and traditional cigarettes may be associated with greater nicotine dependence.