Research area, country of origin, and funding source
The proportion of neurosciences & neurology and pharmacology &
pharmacy articles decreased over time. Substance abuse articles were
uncommon in the first two periods before spiking in the third period.
The other research areas did not show a clear trend over the three time
periods. In all three periods, more papers were published in the US and
Canada than in the rest of the world. The proportion of papers published
in the US and Canada stayed relatively constant in the first two periods
before spiking in the third period. Most citing papers (79%) had no
disclosed funding source. The largest funder of research was the
National Institute on Drug Abuse, which funded 35% of citing articles
with known funding sources.