The agency is to oversee all global PR for varenicline, a yet-unapproved drug that relieves nicotine cravings and reduces withdrawal symptoms.
CCA won the business after a pitch against two undisclosed agencies.
Lisa Stockman, who leads the account for CCA in the US, predicted the drug was 'going to be as big as Viagra for the company'.
The drug is likely to compete with the likes of Acomplia, the hotly anticipated drug from Sanofi-Aventis being trialled for both smoking cessation and obesity.
Varenicline is in phase III clinical trials; in one phase IIa study almost half of smokers successfully quit after seven weeks, compared with 16 per cent taking placebo.
Forbes last year included varenicline, which targets specific mechanisms in the brain involved in nicotine addiction, on a list of five 'neurological drugs to watch', estimating its sales potential as between $1bn and $2bn.
The drug is one of 12 new compounds Pfizer hopes will compensate for the patent-protection loss on several high-earning products.
Teams in CCA's New York, Washington and London offices are working on the account.
The four-strong London team includes MD Jennie Talman and senior consultant Emma Crozier, engaged in what Talman described as 'mainly' media relations.
Pfizer is not using a PR agency ' at the present time' to handle UK-specific PR for varenicline.