Sigma Healthcare Ltd (ASX: SIG) shares have shot to another record high on Monday, bringing the new year's gains to 15% in the green already.

Shares in the healthcare giant hit a fresh high of $3.05 apiece this morning, surpassing their previous closing high of $3.00 last Friday.

Zooming out, the stock is up more than 216% in the past 12 months,

What's next for Sigma shares? Let's see what the experts think.

Why are Sigma shares climbing?

Taking a step back, Sigma shares have rallied this past year thanks to its 'back-door merger' with Chemist Warehouse.

After a series of setbacks, including scrutiny from the Australian Competition and Consumer Commission (ACCC), the regulator approved the merger late last year.

For reference, Chemist Warehouse first mentioned plans to merge with Sigma via the 'backdoor listing' last year. The deal was for Sigma to buy all of Chemist Warehouse's shares, effectively creating an indirect way for Chemist Warehouse to list its stock through the 'back door'. This is why it's known as a back-door listing.

Meanwhile, a scheme booklet outlining the deal's benefits suggested the combined group's FY24 operating profit could hit $605 million before accounting for any synergies.

In FY24, Sigma booked operating profit of $23 million, up 20% from the year prior. So the new entity is expected to grow operating profit by more than 27 times.

The merger's completion in November-December last year prompted feverish buying, with Sigma shares up 10% in the past month alone. Based on those estimates, it's not difficult to see why.

Is it too late to buy Sigma shares?

Investors are undoubtedly bullish on the newly formed entity's prospects, judging by how much Sigma shares have been bid up these past two months.

The proposed financials explain some of this in my opinion, especially given the jump in operating profit.

But brokers are optimistic, too. In December, according to The Australian, Morgans rated Sigma a buy, noting the potential value of the merged business.

Meanwhile, Barrenjoey analysts said the new group could see a doubling of earnings by FY28, as reported by The Australian Financial Review.

Not all are convinced, however. Alternative asset manager HMC Capital Ltd (ASX: HMC) trimmed its stake in Sigma the day the merger was confirmed.

The firm reduced its holding from more than 10.5% to just under 8.25%.

Meanwhile, the consensus of analyst estimates rates Sigma a sell, according to CommSec.

Safe to say, the opinion is split among the experts right now.

Foolish takeaway

Sigma shares are riding high on optimism from its Chemist Warehouse merger.

But brokers are split on where to next from here. Morgans and Barrenjoey are bullish, but others aren't convinced. Time will tell what happens to the newly formed healthcare group from here.