Powder cocaine and crack cocaine are simply two different chemical forms of cocaine. Powder (also called hydrochloride) cocaine dissolves in water and, when used, can be administered by intravenous (by vein) injection or by snorting (through the nose). Crack cocaine is the street name given to a form of cocaine that has been created by dissolving powder cocaine in water, mixing it with baking soda, and heating it to form a hard but volatile (i.e., smokable) mass. The name "crack" comes from the crackling sound that this form makes when it's smoked.
In spite of these differences, cocaine, in any form, produces the same effects once it reaches the brain. It produces similar physiological and psychological effects, but the onset, intensity, and duration of its effects are related directly to the method of use and how rapidly cocaine enters the brain. Smoking crack or injecting cocaine intravenously produces the quickest and highest levels in blood and in the brain, and the effects also wear off the fastest. Repeated cocaine use, no matter how you take it, can produce addiction and other adverse health consequences, especially to the cardiovascular system.
Cocaine belongs to a class of drugs called stimulants, because they usually make you feel euphoric, energetic, hyperstimulated, and mentally alert. The high from snorting may last 15 to 20 minutes, while smoking may last 5 to 10 minutes. Cocaine can also make you feel hypersensitive to touch, sights, and sounds. Some people report feelings of restlessness, irritability, and anxiety. Some of the immediate effects after using cocaine include constricted blood vessels, dilated pupils, and increased heart rate and blood pressure. Heavy doses can lead to violent behavior and people may experience tremors, vertigo, muscle twitches, and paranoia. As a person begins to increase the dose and/or the frequency of drug taking the duration and intensity of the high may lessen, and once it is over, they can feel very tired and depressed. Cocaine is a powerfully addictive drug, and while it can make you feel high when you first use it, addiction is a very real possibility. Naturally, the wisest move is never to start.
See http://www.drugabuse.gov/publications/research-reports/cocaine-abuse-addiction for more information.
Research has revealed a potentially dangerous interaction between alcohol and cocaine. Taken in combination, the two drugs are converted by the body to cocaethylene. Cocaethylene has a longer duration of action in the brain and is more toxic than either drug alone. It is noteworthy that the mixture of cocaine and alcohol is often seen in emergency room (ER) visits that involve drugs. In fact, cocaine is the drug most often mentioned in combination with alcohol in these cases.