Haleon, the consumer healthcare unit spun off by British drugs giant GlaxoSmithKline, began trading on Monday in London's biggest stock market listing for more than a decade.
The new independent company – which owns brands including Sensodyne toothpaste, pain relief drug Panadol and cold treatment Theraflu – was worth around £30 billion (€35bn).
It was the capital's biggest listing since Swiss mining giant Glencore was valued at £38 billion on entry in 2011.
Haleon had expected to debut, however, with a market capitalisation of around £40 billion.
The demerger overseen by GSK chief executive Emma Walmsley is aimed at allowing the pharmaceuticals group to focus on its core business.
Walmsley has faced intense activist shareholder pressure over GSK delays in producing COVID jabs and treatments.
"It's day one of our new era and our new purpose: we're now 100% focused on biopharma innovation, uniting science, technology and talent to get ahead of disease together," GSK wrote on Twitter.
Haleon meanwhile described its entry onto the London stock market as "the biggest UK listing in a decade".
Victoria Scholar, head of investment at Interactive Investor, said the listing was "a win for the London Stock Exchange post Brexit, given that the UK stock market has been overly reliant on commodity and financial businesses.
"However for Haleon, there's no doubt this is an extremely challenging time to come to market, with this year's equity market volatility."
Scholar added that is was "also a challenging time for the consumer health sector, given that inflation is close to double digits in the UK and in the US".
Haleon will also trade on the New York Stock Exchange.
The consumer healthcare company, whose portfolio of products includes also Centrum multivitamins and anti-inflammatory Voltaren, generates annual sales of about £10 billion.
GSK, which owned 68 per cent of Haleon, plans to retain six per cent of the group.
US pharmaceutical titan Pfizer has said it plans to sell its 32 per cent minority stake.
Walmsley, who had led the consumer unit prior to her promotion as head of GSK in 2017, sees more long-term value in the demerger than a sale.
At the start of the year, GSK rejected a £50 billion bid for the unit from consumer goods titan Unilever.
"GSK shot themselves in the foot by not accepting" the bid, Michael Hewson, chief market analyst at CMC Markets UK, told AFP on Monday.
"GSK shot themselves in the foot by not accepting” a £50 billion bid for the unit from consumer goods titan Unilever- Michael Hewson, chief market analyst at CMC Markets UK
At the same time, "£30 billion is still a pretty decent valuation given the cost-of-living crisis".
Different paths
Walmsley, part of a group of less than 10 women chief executives running companies on London's top stock market index, the FTSE 100, has described the demerger as the group's most significant corporate change in two decades.
Alongside the split, GSK is expanding further into the field of vaccines. In May it snapped up US biopharmaceutical firm Affinivax for up to $3.3 billion.
Also this year, the British company spent $1.9 billion on US group Sierra Oncology, a specialist in medicines for rare forms of cancer.
Haleon chief executive Brian McNamara said the standalone company stood "ready to help address consumer needs".
"Consumer health has never been more important than it is today, and I am delighted that Haleon, as an independent company, is ready to pursue" its ambitions.
Haleon will be headquartered in Weybridge, southwest of London.