From the song; '
Hey Boys and
Girls' by Evermore.
This is perhaps best understood as a commentary on the use of socially accepted mind-altering drugs, the most famous of which are probably Prozac and Ritalin. Note how the lyrics say it "makes me
happy" and "now I'
m awesome" which strongly suggest it affects the user's mood.
The literal meaning of "truthagen" would be something that generates
truth, which while nonsensical is generally positive-sounding. This term is probably a further commentary on the nonsensical names of designer drugs such as the aforementioned Prozac and Ritalin.