The suppression field's main effects are to bring the human birth rate down to zero by prohibiting "certain protein chains important to the process of embryonic development", as Dr. Isaac Kleiner states in Episode One, making it utterly impossible for conception to occur in any form. This effectively ensures that the humans currently alive would be the last naturally born generation. When in proximity to the abandoned playground, the echoing sounds of children screaming can be heard, an eerie scene depicting the result of the suppression field. Doctor Breen addresses the issue of the suppression field to the people via a broadcast during the early levels of Half-Life 2, as the response to a letter written to him by a "concerned citizen", and claims that the field will be deactivated once the humans prove they no longer need it. However, ultimately, this is likely part of his propaganda grandstanding with the real implication being that people won't care about breeding after "they crawl out of the dark pit of our species' evolution" and "reap the benefits of the universal union" such as "immortality".
It is unknown precisely how the suppression field affects humans. The suppression field somehow prevented human sexual urges according to Dr. Breen's statement that it was suppressing "the urge to reproduce". A speech by Dr. Kleiner in Half-Life 2: Episode One makes reference to protein chains being unable to form under the field, implying that the field forced biological sterility.
In Half-Life 2: Episode One, it is revealed by Isaac Kleiner during his hijacked broadcasts throughout the city that with the near destruction of the Citadel, the suppression field had been disabled. He suggests that everyone, "should give serious thought to doing their part for the revival of the species", if they have escaped City 17. Also in Episode One, a Resistance fighter mocks how since the suppression field is down she has permission to mate, quoting "Not that I needed permission anyways", which might mean that the suppression field allows humans to mate, just not reproduce. Alyx comments on the unusual nature of this directive with, "Is Dr. Kleiner really telling everyone to... 'get busy'?". Also, in Half-Life 2: Episode Two, when Alyx and Gordon reach White Forest and meet Eli, Alyx says she and Gordon make a good team. With a wink and a nod, Eli says to Gordon "You know with the suppression field down, we all have to do our... part". After an embarrassed outburst from Alyx, he says, "Can you blame an old man for wanting grandkids?".
List of appearances
- Half-Life 2 (First appearance) (Abstract appearance only)
- Half-Life 2: Episode One (Abstract appearance only)
- Half-Life 2: Episode Two (Abstract appearance only)