Sigma Healthcare has moved closer to its $8.8 billion merger with Chemist Warehouse after offering hundreds of its franchisees an exit path from the group if the deal goes ahead, in a bid to appease competition concerns.

The concession added almost $1 billion to Sigma’s market capitalisation on Tuesday after its shares rallied 23 per cent to an 18-year-high, with investors betting the Australian Competition and Consumer Commission might approve the merger without forcing the pharmacy giants to sell stores.