Complex sentence: Some studies of continued use of nicotine replacement products in those who have stopped smoking found no adverse effects from months to several years, and other studies suggest that people with cardiovascular disease were able to tolerate them for up to 12 weeks.
Split into simpler sentences: Some studies of continued use of nicotine replacement products in those who have stopped smoking found no adverse effects from months to several years. Other studies suggest that people with cardiovascular disease are able to tolerate nicotine replacement products for up to 12 weeks.