Sales of Suboxone have slumped and Reckitt has two new pharmaceutical projects that could diversify revenue and boost the unit's market valuation.

The British company put Suboxone under strategic review in October and in April said it was leaning towards spinning off the business rather than a private sale.

Analysts had given a range of valuations for the business due to uncertainty over the longer-term impact of competition from generic versions of Suboxone. Deutsche Bank values it at 2.9 billion pounds ($4.92 billion) including debt. Prior estimates from other analysts have ranged from 2 billion to 5.5 billion pounds.

"A trade buyer looks to have remained elusive, with a stock market listing the natural, if potentially more fraught, alternative," said Hargreaves Lansdown analyst Keith Bowman.

Reckitt did not entirely rule out an outright sale if a buyer emerges. It has not decided whether to keep a stake in Suboxone if it opts for a spin-off.

Reckitt, which also makes Durex condoms, Finish detergent and Nurofen painkiller, reported a 4 percent rise in first-half sales on a constant-currency basis, excluding Suboxone, whose sales fell 8 percent.

The growth was in line with many analysts' expectations.

Reckitt stood by a 2014 target for revenue growth of 4-5 percent this year. It said it expected more profit margin growth, which implies an increase on a prior target for the margin to be flat to marginally higher.

Recent efforts to reduce costs have targeted the company's advertising budget, among other areas.

Reckitt shares were up 2.6 percent at 0821 GMT (9.21 a.m. BST).

Bernstein analysts have said that Suboxone - which is sold as a film that dissolves in the mouth - has 79 percent of the large U.S. market, down from about 85 percent since generics went on sale in March last year.

(Reporting by Martinne Geller in London; editing by Tom Pfeiffer)