Here's as much detail as I can remember:

• I saw the film at the Irish Film Institute in Dublin, Ireland (IFI) within the past 15 years.
• The IFI tends to show independent / arthouse films that aren't generally available to see in mainstream cinemas
• The film plot was about a man who appears to work in an ordinary desk job. However, overtime he starts to notice usual events and becomes suspicious. Eventually he finds out that a pharmaceutical company are secretly testing new drugs on him and that his 'job' is completely fake - just a way for them to monitor him.
• I remember one scene in particular where he is on business (perhaps on an airplane supposedly on a business trip or at a conference venue), After a short time all of the people in the plane / room are sedated but somehow the main character stays awake. He sees all of the pharmaceutical technicians testing the unconscious people.
• I'm about 80% sure it was based in the U.S. or at least had actors with American / Canadian accents
• The Constant Gardener is the main film that appears after I google this and that's definitely not it.
• I really enjoyed the film. I'd love to know what it is so I can watch it again and recommend to others.

Thanks!