Connecticut is joining other states in investigating vaping manufacturer Juul Labs.

State Attorney General William Tong says the state wants to determine if Juul is illegally marketing its products as smoking-cessation devices and whether it has properly limited its marketing to adults.

Tong says the state's investigation is part of a national effort to curb youth vaping. That includes a lawsuit over Juul's marketing practices in North Carolina and similar investigations in other states.

He says Connecticut is targeting Juul because it has the largest share of the vaping market.

Tong says Juul's products have never been approved by the U.S. Food and Drug Administration as smoking-cessation devices and should not be marketed as such.

Juul spokesman Theodore Kwong says the company's product is not intended to help people quit nicotine.

Follow NBC HEALTH on Twitter & Facebook.