What is caffeine?
Caffeine is a stimulant that people ingest in order to get a boost of energy.  One of the most common forms of ingested caffeine is coffee.  Caffeine gives you energy for a short while but it is often followed up with a feeling of being tired, sleepy or lethargic.  People use caffeine as a performance enhancer, mood and brain booster and increased alertness.
Below is an instruction that describes a task, paired with an input that provides further context. Write a response that appropriately completes the request.
### Instruction: What is caffeine?
### Input: 
### Response: Caffeine is a stimulant that people ingest in order to get a boost of energy.  One of the most common forms of ingested caffeine is coffee.  Caffeine gives you energy for a short while but it is often followed up with a feeling of being tired, sleepy or lethargic.  People use caffeine as a performance enhancer, mood and brain booster and increased alertness.