What are stimulants? List one stimulant and its source.

Explanation

### Step-by-Step Solution:

1. **Definition of Stimulants**: Stimulants are substances that increase the activity of the central nervous system (CNS). They enhance brain function, leading to increased alertness, attention, and energy levels.

2. **Effects of Stimulants**: These substances can induce feelings of excitement, elevate mood, and inhibit sleep. They are often used to combat fatigue and improve concentration.

3. **Contrast with Depressants**: It is important to note that stimulants are the opposite of depressants, which decrease CNS activity and can induce relaxation or drowsiness.

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