In an announcement made Thursday, Pfizer Inc, defended its drug, Chantix, prescribed to help smokers break the desire for nicotine. Chantix has been linked lately to thoughts of suicide and depression when taken by people who suffer from mental illness.

Chantix - vareniclineSaying there is no reason why people should not take Chantix even though they have a history of mental illness, Dr. Martina Flammer, the pharmaceutical company’s senior medical director, urges patients to notify their prescribing physician of any mental conditions before taking the drug.

The US Food and Drug Administration (FDA) first began investigating the drug after reports were filed that described psychiatric events, including suicidal thoughts, from patients taking Chantix. The FDA investigation led to labeling changes for Chantix that call for monitoring a patient for unusual behaviors.

In May, the Federal Aviation Administration (FAA) declared a ban on the use of the prescription drug for all pilots and air traffic controllers. The ban came after a report from a non-profit group issued warnings of serious side effects associated with Chantix.

Unlike Zyban, another drug prescribed to quell the urge to smoke, Chantix binds itself to the same receptors in the brain that nicotine does, thereby blocking the ability of nicotine to bind to these receptors. In the process, Chantix triggers the release of dopamine, a chemical known for causing feelings of euphoria. Zyban interacts with chemicals that occur naturally in the brain and does not interfere with the brain’s nicotine receptors.

In its Thursday announcement, Pfizer said it is in the process of conducting additional studies that include people diagnosed with schizophrenia as well as those with heart disease, emphysema, and adolescents. The company announced plans to release detailed analysis by the end of the year of any psychiatric events documented in any patient using Chantix.

Pfizer claims its earlier independent studies produced no increased incidence of psychiatric event in people taking Chantix versus a placebo but David Gonzales says the earlier trials deliberately excluded schizophrenics and other patients with mental illnesses. Gonzales led the earlier trials and is co-director of the Smoking Cessation Center at Oregon Health & Science University.

During 2007, Pfizer’s pharmaceutical sales revenue topped $44 billion, $883 million of which came from the sales of Chantix, one of its newest and best-selling drugs.