What are substances?

Some articles on substances:

Controlled Substances In Oregon
... The most used substances were marijuana, methamphetamine and illicit painkillers and stimulants ...
Shennong Ben Cao Jing - Content
... The second volume was devoted to 120 therapeutic substances intended to treat the sick, but more or less toxic ... The substances of this group are described as "human." In the last volume there are 125 entries corresponding to substances which have a violent action on physiological functions and ...