The amount of nicotine in e-cigarette fluid varies. Some research has found that e-cigarettes deliver less nicotine on average than traditional cigarettes,93 but that users may change puffing patterns to compensate. Inexperienced e-cigarette users take in modest nicotine concentrations, but those who regularly use these devices adjust their puffing to consume similar levels of the drug as with traditional cigarettes.93–95 Newer e-cigarette devices can deliver substantial amounts of nicotine, and some users are able to get nicotine at levels similar to96 or even greater than a traditional cigarette.97,98 One study found equivalent levels of nicotine's major metabolite in the blood of smokers who use traditional and e-cigarettes.89 Thus, all the nicotine-related concerns of traditional cigarettes—addiction, effects on cognitive function, and effects on prenatal development—apply to e-cigarettes as well.