Nicotine-free vapes could be lying to their customers.

Tests have revealed that some vape products which claim to omit nicotine actually contain the same amount of addictive substances as a full-strength e-cigarette.

Inter Scientific, a quality control laboratory that ensures consumer goods meet legal requirements, looked at dozens of vape brands found on store shelves across England and Wales.

Of the 52 products they analyzed, researchers found that most oversized and extra-strength vapes are being sold illegally, according to data provided to the Guardian.

“We have seen a large increase in the number of illegal vape products being seized by trading standards and sent for analysis. Though these products don’t pose an immediate health risk, they are circumventing UK regulation,” David Lawson, chief executive at Inter Scientific and a fellow of the Organization for Professionals in Regulatory Affairs, said.

The UK’s Tobacco Products Directive states that the legal tank capacity for a “disposable electronic cigarette, a single-use cartridge or a tank” should be no more than 2 milliliters of vape liquid.

Data showed that a majority of products — 73% of the study pool — exceeded the TPD’s limit, and more than 40% had been filled with five milliliters or more.

Eight of the products that claimed to be nicotine-free indeed did contain some of the substance, often meeting the legal limit of 20 milligrams of nicotine per milliliter, while one device turned up 50% more nicotine than the UK’s regulatory cutoff.

Although the US hasn’t set any strict standards for vape manufacturing, brands sold in the States may have a nicotine content between 3 and 36 mg/ml, and up to 60 mg/ml.

Definitive research on the health effects of e-cigarettes remains ongoing, with some experts suggesting that the cigarette alternative could be a powerful tool to help tobacco users quit smoking. However, recent studies have suggested that vaping could be a risk factor for lung disease, heart disease, diabetes, mental illness, sexual dysfunction and even eyesight.

Meanwhile, US policymakers are cracking down on e-cigarette advertising, which they say has unscrupulously marketed potentially unsafe products to kids and teens. Following years on trial, vape maker Juul agreed last week to pay $462 million to several states after being sued for causing a “vaping epidemic” among kids.

In June of last year, the Food and Drug Administration opted to ban the sale of Juul e-cigarettes in the United States, but the motion was put on hold while the FDA reconsiders Juul’s appeal.

About 8% of Americans vaped in the past week, according to a recent Gallup poll, competing with cigarette smokers at 11%. But among the adolescent cohort, the FDA has found that e-cigarettes rule the school with 9.4% of teenage students reporting having used a vape during the past month.