GSK shares plummet 20%! What’s going on here?

GSK shares fell on Monday morning on the back of a demerger and a consolidation. So maybe this represents a buying opportunity?

The content of this article was relevant at the time of publishing. Circumstances change continuously and caution should therefore be exercised when relying upon any content contained within this article.

Young female analyst working at her desk in the office

Image source: Getty Images

You’re reading a free article with opinions that may differ from The Motley Fool’s Premium Investing Services. Become a Motley Fool member today to get instant access to our top analyst recommendations, in-depth research, investing resources, and more. Learn More.

GlaxoSmithKline (LSE:GSK) shares were the FTSE 100‘s biggest faller on Monday morning. The stock fell following its long-planned demerger and the listing of Haleon (LSE:HLN), with the consumer healthcare spin-off becoming one of Europe’s largest listing in more than a decade.

So why is the share price falling, and does this represent an opportunity for me to buy?

Why is the share price falling?

GSK stock fell after the London-based multinational pharmaceutical and biotech firm’s demerger went live. Investors who had stock in Glaxo will now receive shares in the consumer healthcare company.

Haleon, which is now the largest consumer healthcare business in the world, opened with a share price of 330p, giving it a market value of about £31bn. Is it poised to join the FTSE 100, qualifying it in terms of market-cap by some distance.

As such, GSK shares should be falling by an equivalent value with shareholders reimbursed by the award on Haleon shares. Glaxo is currently down 343p. But with Haleon shares worth 330p, the fall is roughly cancelled out by the Haleon listing.

However, Glaxo has decided to complicate matters for everyone involved by also undertaking a consolidation. The thing is, nobody knows exactly what this consolidation is going to look like. It will take place after close of trading on Monday, returning the share price to roughly the same as before the demerger.

Therefore, valuing GSK shares is quite difficult right now.

Demerger benefits

The demerger has been touted as an opportunity for Glaxo to push forward after a sustained period of underperformance. For years, GSK has operated as a pharmaceutical company with a huge consumer healthcare business trading in a fast-moving retail segment that is largely reliant on marketing everyday products to customers.

Pharmaceuticals is very different. The industry requires years of research and trials before a product is finally brought to market. At which point it is sold not to regular consumers, but to governments and healthcare trusts.

As such, the two businesses are not necessarily well aligned.

The demerger should allow GSK to focus on vaccine and drug development. However, the failure of the firm to make its own Covid-19 vaccine during the pandemic is perhaps a reflection of its underperformance in recent years.

Would I buy GSK shares?

I’d buy Glaxo shares at the current price ahead of what will hopefully be a new era of prosperity for the pharma giant.

There are several reasons for this. Firstly, the demerger has clear benefits for both businesses. But secondly, I’m fairly bullish on pharmaceuticals over the long run. With ageing populations in the West, there is increasing need to invest in lifesaving medicines. It’s all about the prolonging the period of healthy lives.

Moreover, for sometime, GSK has also been undervalued verses its peers although the Haleon spin-off and consolidation makes valuation a little difficult right now. It also boasts a healthy dividend yield around 4.2%.

Supply chain issues and inflation pushing up costs are certainly issues to contend with, but I’m still bullish for a GSK renaissance.

James Fox has no positioned in any of the shares mentioned. The Motley Fool UK has recommended GlaxoSmithKline. Views expressed on the companies mentioned in this article are those of the writer and therefore may differ from the official recommendations we make in our subscription services such as Share Advisor, Hidden Winners and Pro. Here at The Motley Fool we believe that considering a diverse range of insights makes us better investors.

More on Investing Articles

Investing Articles

The key number that could signal a recovery for the Greggs share price in 2026

The Greggs share price has crashed in 2025, but is the company facing serious long-term challenges or are its issues…

Read more »

Rolls-Royce's Pearl 10X engine series
Investing Articles

Can the Rolls-Royce share price hit £16 in 2026? Here’s what the experts think

The Rolls-Royce share price has been unstoppable. Can AI data centres and higher defence spending keep the momentum going in…

Read more »

Businessman with tablet, waiting at the train station platform
Investing Articles

Up 150% in 5 years! What’s going on with the Lloyds share price?

The Lloyds share price has had a strong five years. Our writer sees reasons to think it could go even…

Read more »

Investing Articles

Where will Rolls-Royce shares go in 2026? Here’s what the experts say!

Rolls-Royce shares delivered a tremendous return for investors in 2025. Analysts expect next year to be positive, but slower.

Read more »

Emma Raducanu for Vodafone billboard animation at Piccadilly Circus, London
Investing Articles

Up 40% this year, can the Vodafone share price keep going?

Vodafone shareholders have been rewarded this year with a dividend increase on top of share price growth. Our writer weighs…

Read more »

Buffett at the BRK AGM
Investing Articles

Here’s why I like Tesco shares, but won’t be buying any!

Drawing inspiration from famed investor Warren Buffett's approach, our writer explains why Tesco shares aren't on his shopping list.

Read more »

Investing For Beginners

If the HSBC share price can clear these hurdles, it could fly in 2026

After a fantastic year, Jon Smith points out some of the potential road bumps for the HSBC share price, including…

Read more »

Investing Articles

I’m thrilled I bought Rolls-Royce shares in 2023. Will I buy more in 2026?

Rolls-Royce has become a superior company, with rising profits, buybacks, and shares now paying a dividend. So is the FTSE…

Read more »