While the company insists its smoking alternatives are less harmful than cigarettes, some health groups have expressed concern that heat-not-burn products expose consumers to other toxins and argue long-term effects are not yet known.
The US Food and Drug Administration approved IQOS for sale in the US last year, though stopped short of ruling whether it can be marketed as less risky than cigarettes.
The company set a target three years ago that at least 40 million adult smokers will have stopped smoking and switched to its smoke-free products by 2025.
Philip Morris estimates nearly 14 million consumers were IQOS users at the end of 2019, with almost 10 million having quit cigarettes. There are some 1.3 billion tobacco users globally, according to the World Health Organisation.