E-cigarette sales have been declining in recent months, after five years of rapid growth, according to The Wall Street Journal.

Among the reasons for the decline are customer dissatisfaction, backlogs of inventory, state laws and concerns over safety, the article notes.

The rate of e-cigarette growth is expected to be 57 percent in the next six months, down from its compound annual growth of 114 percent over the past five years, the research firm Euromonitor International predicts.

The sharpest decline in sales has been among large tobacco companies’ devices that resemble cigarettes. Sales of those devices decreased 21 percent during the 12-week period that ended October 31. In July, tobacco maker Reynolds American told investors it would miss its goal of making its Vuse e-cigarette brand profitable in the second half of 2015.

The bigger, refillable devices known as vaporizers, sold at independent vape shops, also have experienced slower sales. Vaporizer sales are expected to increase 51 percent next year, down from 126 percent in 2015, and 455 percent from 2013 to 2014.

Some users find e-cigarettes disappointing because they don’t deliver nicotine into the bloodstream as fast as cigarettes, and don’t offer the same “throat hit” that cigarettes provide, the newspaper notes.

The e-cigarette industry is awaiting final rules from the Food and Drug Administration (FDA) on regulating e-cigarettes. The agency proposed rules in April 2014 that would ban the sale of e-cigarettes, cigars and pipe tobacco to anyone under age 18.

Manufacturers of e-cigarettes and cigars would have to register with the FDA, give the agency a detailed account of the products’ ingredients, describe their manufacturing process and scientific data, and submit to FDA inspections. Companies would no longer be allowed to offer free samples. E-cigarettes would be required to come with warning labels stating they contain nicotine, which is addictive.