Jenkins will leave at the end of August to become a freelance consultant.
Corporate affairs director Gill Markham said the firm was seeking to replace her.
Jenkins acted as Markham’s deputy, handling day-to-day relationships with the firm’s agencies, which include Red Door Communications, Athena, Medical PR and Jango Communications.
Markham added: ‘We are the third-largest [drugs company] in the UK in terms of sales, but that comes as a surprise to some people. We are better known for our individual products, but the aim of PR going forward is to raise awareness of Wyeth.’
Wyeth products include gastrointestinal treatment Zoton and anti-depressant Efexor XL.