The French broker also cut its target price for the Dettol disinfectant to Nurofen painkillers firm to 5,600p from 7,300p, with the shares down 0.3% to 6,345p in morning trade.
In a note to clients, SocGen’s analysts said the company needs to "cross the chasm" into mass market positions to reignite growth, which should impact on its margins.
They forecast Reckitt’s margins contracting by 180 bp (basis points) to less than 25% by 2021.
The analysts said they do not expect the group’s 2.9% full-year 2018 growth to be improved on this year, as Reckitt’s underlying sales growth has been 2.5%-3.0% per annum for the past five years.
They added that they see Reckitt posting organic sales growth of 2.5% in full-year 2019.