“In 1975, less than half the world’s population were estimated to have regular access to essential medicines. New estimates from the 1999 World Medicines Survey show that this fraction has fallen to around one-third. However, the absolute number of people without access has remained almost unchanged, at about 1.7 billion. Getting the right medicines to the people who need them at the time they need them remains a major challenge.”
(Newest estimate as far as I know)
WHO World medicines situation 2004
Notes: I chose the 2004 report because it has the most clear quote and says where it comes from (the 1999 WMSurvey). Here is the 2011 World Medicines Situation report.