Crack cocaine has telltale signs of use. Someone on the drug will exhibit excessive and perhaps uncharacteristic bursts of energy and stimulation, going far beyond any reasonable kind of excitement. The manic activity may include things like talking rapidly, consuming food at an inhuman rate (or perhaps not even needing food at all, despite having gone without sustenance), or being otherwise nervously agitated. When the dose wears off, users show signs of great fatigue, sometimes falling asleep wherever they are and then staying asleep for days.
The drastic seesawing between unstoppable energy and exhaustion has obvious impacts on day-to-day behavior. Crack cocaine renders regular sleep habits all but impossible, in turn throwing off regular attendance at school, work attendance, and other obligations. The superhuman stimulation and unfathomable fatigue also cause violent and unpredictable mood swings, causing users to be argumentative and perhaps violent and dangerous to those around them, especially toward people who try and stop the drug use. Being off crack for a while can cause severe depression and even suicidal thoughts. Abusing crack for a prolonged period of time can lead to paranoia and hallucinations.
In fact, the incessant trembling may convince some users that if they had more crack, they would be able to control the jitters or not care about them at all, which then compels them to seek out and use more crack.
Seeking out crack is, in itself, a sign of an addiction – not only because an addict wants it, but because the addict wants the drug even though it is painfully obvious that the habit has caused a lot of problems. For most people, discontinuing a habit when the disadvantages outweigh the benefits is a logical course of action. For someone addicted to a substance, thinking that clearly and objectively is not always easy.
Someone addicted to a drug as powerful as crack cocaine will either vehemently deny that the drug is the cause of their problems or be helpless to control their intense physical and psychological compulsion for more of the same.