Sigma Pharmaceuticals Ltd (ASX:SIP) has agreed to hand its pharmaceuticals division to South Africa's Aspen Pharmacare Holdings Ltd for $900 million.

After considering a few expressions of interest in the firm's business and parts of the group, "The Board has concluded that Aspen's proposal to acquire the Pharmaceuticals division is the best alternative for Sigma shareholders," Sigma chairman Brian Jamieson said in a statement on Monday.

Sigma's pharmaceuticals division include generics, consumer, over-the-counter, Herron, ethical and medical products, Orphan and manufacturing businesses.

The proposed deal with Aspen was subject to a number of conditions, including approval from shareholders, lenders, and regulatory board, and preparation of definitive sale documentation.

Sigma's board of directors advised shareholders to vote in favour of the sale in the absence of a better alternative.

The Australian company would retain its healthcare division, which covers the wholesale and retail businesses under the proposed term.

"Sigma will emerge after the sale in a financially powerful position for future growth and business improvement under the company's new management team led by Mr Mark Hooper," Mr Jamieson said.

"We will also consider potential capital management initiatives."

Sigma stocks gained 3.5 cents, or 7 per cent, at 54 cents by 1022 AEST.