Pfizer, the world’s largest drug maker, said Wednesday that it paid about $20 million to 4,500 doctors and other medical professionals for consulting and speaking on its behalf in the last six months of 2009, its first public accounting of payments to the people who decide which drugs to recommend.

Pfizer also paid $15.3 million to 250 academic medical centers and other research groups for clinical trials in the same period.

While other pharmaceutical companies have disclosed payments to doctors, Pfizer is the first to disclose payments for the clinical trials. The disclosure does not include payments outside the United States.

A spokeswoman for Pfizer, Kristen E. Neese, said most of the disclosures were required by an integrity agreement that the company signed in August to settle a federal investigation into the illegal promotion of drugs for off-label uses.