Final answer:
Benzedrine is considered toxic due to its potential for abuse at high doses and the serious health risks it poses, including dependence and long-term adverse effects on cognitive function and mental health.
Step-by-step explanation:
Benzedrine, a brand of inhalers, was the first pharmaceutical amphetamine and is known to have a range of effects at different doses. At therapeutic levels, Benzedrine can improve cognitive control and resistance to fatigue, but at higher, non-therapeutic doses, it can cause significant health problems including dependence and psychosis. Considering the potential for abuse and the health risks associated with high doses or long-term exposure, Benzedrine would likely be classified as a toxic substance. Therefore, the correct answer is 4) toxic.