Slough-based Reckitt said it was considering "all options" for the drugs business, which is valued by some analysts at more than £2.5 billion.
The pharmaceutical division is based in the United States and focuses on its Suboxone heroin addiction medicine - a treatment that is now facing competition after the recent launch of two generic rival tablets .
Revenues at the division stood at £191 million in the third quarter, down 16% on a constant currency basis.
Reckitt has previously said the launch of generic tablets would mark the right time to consider its options for the pharmaceutical business.
But it cautioned the review would "take some time" and plans to update shareholders in 2014.
Reckitt shares rose 5% as investors welcomed a possible sale of the unit.
The group also made a marginal increase to its full-year net revenue outlook, pencilling in growth of at least 6% from previous guidance of 5% to 6%, thanks to a boost from recent acquisitions in the third quarter.
Martin Deboo, analyst at Investec, said the pharmaceutical review signalled a "strong intent to sell".
He said the business could be valued at between £2.5 billion and £5.5 billion.
Panmure Gordon experts added: "Whilst Suboxone has delivered tremendous profits and cashflow for the group, we think now is the right time to seek an exit."
Reckitt said strong demand helped its cough and sinus congestion medicine Mucinex perform well in a long flu season, which helped comparative revenues in the health division rise by 12% in the first nine months.
Hygiene product sales - such as Dettol and Harpic - rose 7% in the year to date, while home brands edged 1% higher after air freshener Airwick was hit by competition and Vanish saw weak demand across Europe.