They are grouped in the chemical classifications of Stimulant, Depressant, and Hallucinogen. Smoking Caffeine Lasts 2 - 4 hours.
Large doses can delay sleep.
Restlessness, upset stomach. Can be harmful for people with heart problems. Oral Amphetamine Speed Picture Lasts 4 - 8 hours. Larger doses delay sleep. Harmful Inability to sleep, restlessness, headaches, aggression.