Department of Health officials confirmed that the campaign, which has a $3.8 million spend on media, began on March 28 and will finish on April 13.

The total cost of the campaign will be $5.6 million.

The timing decision was made by the department in conjunction with Health Minister Greg Hunt.

The department had $19.5 million to spend on advertising over the financial year and the PBS campaign is the biggest in the health portfolio.

The television, newspaper, radio and online campaign aims to teach Australians about the PBS and how it keeps medicines affordable.

"The campaign is focusing on raising awareness of the role of the PBS and the importance of providing low-cost, disease-preventing and life-saving medicines to consumers," department deputy secretary Matt Yannopoulos told a Senate estimates hearing in Canberra on Wednesday.

"In terms of timing, we began the research phase for this in mid-December last year."

Department officials denied the timing of the campaign was linked to the forthcoming election, which is expected to be held on either May 18 or May 25.

A senior Treasury official told a separate Senate committee the department's main ad campaign explaining the government's tax changes was due to wrap up on Saturday.

Deputy secretary Matt Flavel said the timing for the $16 million, 12-week series of ads across radio, television and newspapers had been set when it first aired on January 20.

Australian Associated Press