Here is a web page from The London School of Medicine and Dentistry, which I think is supposed to train medical students about risk, and which uses Champix as a case study: Champix
It summarizes the "controversy", including individual anecdotes:
Musician Carter Albrecht was shot and killed by his girlfriend's neighbour.
... and actions by regulatory bodies:
The New York Times reported that the U.S. Federal Aviation Administration (F.A.A.) had announced the day before a ban on the use of Champix (varenicline tartrate) for both pilots and air traffic controllers, due to concerns with possible adverse neuropsychiatric effects which could be detrimental to public safety.
... and widespread complaints:
In 2009, Health Canada announced that it had received more than 800 complaints from Canadian users, many of them reporting mood swings, depression or suicidal thoughts.
In the United Kingdom Up to 200,000 people take the medicine twice-a-day. The Medicines and Healthcare Products Regulatory Authority (MHRA) say they have received over 800 reports from users of Champix who experienced adverse reactions when using the drug. Not all these adverse reactions were of a psychological nature but included things like nausea, dizziness, vomiting and abnormal dreams.
Nevertheless it ends with:
Despite the controversy, a cohort study published evaluated medical records of 80,660 persons attempting to quit smoking (10,973 of which were using Champix) and found no evidence of an increased risk of depression, self-harm and suicide, although a small increase could not be ruled out on statistical grounds. A study conducted by Group Health Center for Health Studies, SRI International, and Free & Clear, Incorporated, published in the Journal of General Internal Medicine, found that people with a history of depression are not more susceptible to the reported psychiatric side effects of Champix than people with no history of depression.
Despite the controversial use of Champix as a method to quit smoking,
do you think that this medicine should be legal?
Is it worth the risk? Think In terms of not developing adverse
reaction and quitting smoking which is associated with cancer?
I'm not a medical student but my reading of this is that we're meant to understand three things:
Anecdotes aren't worth as much as cohort studies; when you have 200,000+ people taking a drug there are going to be some scary stories.
The cohort study says it's safe (at least regarding depression etc.)
It's less dangerous than smoking