I count the deaths of Mao's "Great Leap Forward" and his communist revolution as a consequence of the societal collapse of China due to drugs.
In other words, if China did not have at one time about 1/2 of it's population addicted to drugs (that can be found at Druglibrary.org) Mao would have never came to power.
The 100 million number I cite is from the known deaths caused by Chairman Mao's rise to power. It is very likely that there were also 100 million deaths which are directly due to drug usage, but I am not aware of any good records which will prove this.
This book has a lot of good information in it on this subject, but it is mostly anecdotal accounts.