Crack is a solid---as opposed to powdered---form of cocaine. Available as white or off-white rocks, crack cocaine is commonly ingested by smoking. Crack is highly addictive, and using it can lead to significant health problems including heart and lung damage. Individuals who use crack often exhibit certain behaviors that you can identify.
Check the eyes. While some drugs cause pupils to constrict, crack causes the pupils to dilate. Excessively large pupils, especially in well-lit rooms, can indicate recent crack use.
Listen to the person's speech. Crack users, especially when still under the influence of the drug, speak in a rapid, excitable manner. Listen to how the person is talking, and if the speed of their speech is inappropriate for the situation, or is not a normal speech pattern for the person, it can indicate recent crack use.
Pay attention to the person's demeanor. Crack causes excitability and agitation in the user. If the person is normally relaxed, but appears unable to sit still or concentrate, it may reveal crack usage. If the person appears agitated, it is possible the drug is wearing off.
Look for personality changes. A crack user will show marked changes in personality. They will become hostile and antagonistic to friends and family members. Their sleep patterns will change, and they may display signs of extreme paranoia. When under the influence of crack, they may act euphoric or manic, but as the drug wears off, they will become sullen, withdrawn and depressed.
Examine the person's personal habits. A crack user will change their personal habits, including eating and grooming. They will often suffer rapid weight loss from lack of eating, and care less about personal appearance or cleanliness.
Keep an eye on your valuables. The highly addictive nature of crack often influences users to acquire money at all costs. If you notice money or valuables missing from your home, it may indicate that a person in your home has started to use crack.
Keep your eyes open for drug paraphernalia. Since crack is most commonly smoked, be aware of the sudden appearance of glass pipes or an excessive number of lighters.