Sigma Healthcare Ltd (ASX: SIG) shares have been on a tear this past year.

Shares in the S&P/ASX 200 Index (ASX: XJO) healthcare stock – which owns chemists including Amcal, Discount Drug Stores, and Guardian Pharmacy – really took off a bit over a year ago, in December 2023.

That's when Sigma first announced its $30 billion merger intentions with privately owned Chemist Warehouse.

As those merger plans progressed throughout 2024 and into 2025, Sigma shares made some ASX investors very happy.

How happy?

Let's have a look.

What $5,000 invested in Sigma shares last December is worth today

If you had a working time machine, you could pop back to 1 December 2023 and snap up Sigma shares for 69 cents apiece.

This means your $5,000 investment would have netted you 7,246 shares (ignoring brokerage fees).

In late afternoon trade today, those same shares are changing hands for $2.75 apiece.

That means the Sigma shares you bought on 1 December 2023 for $5,000, less than 15 months ago mind you, is now worth a whopping $19,926.50. Or a gain of 298.6%.

But we're not quite done with the maths yet.

Adding a little icing to this highly profitable cake, you'd also have received a total of 1 cent per share in partly franked dividends over this period.

Which would bring your total returns on the initial $5,000 investment to $19,998.96.

Now, when you're done with the time machine, can you please drop it by my office!

What's the latest on the pending merger with Chemist Warehouse?

On 30 January, ASX 200 investors learned that, as expected, Sigma shareholders had voted to approve the merger with Chemist Warehouse, with 99.86% voting 'yes'.

Sigma shareholders also agreed to elect four Chemist Warehouse executives to the Sigma board.

The Chemist Warehouse board's vote to approve the merger received 99.23% support.

Commenting on the merger on the day, Sigma chair Michael Sammells said:

Sigma has world-class distribution infrastructure and capability that is delivering best in class service to pharmacies across Australia every day.

Chemist Warehouse has unparalleled pharmacy franchise and marketing know-how and expertise which will also help elevate our support for our Amcal and Discount Drug Store franchisees.

Given the nature and value accretion of the proposed transaction, Sigma Directors unanimously recommend that shareholders vote in favour of the resolutions.

Sigma shares had been in a trading halt the day before and closed down 3.6% following the news.

Though, as we saw above, that hardly crimped the returns investors have reaped since the merger news first broke in December 2023.

The merger process was finalised this afternoon when Sigma announced that its 100% acquisition of issued shares in Chemist Warehouse via a scheme of arrangement was implemented today.