Updated June 20, 2014.

Cocaine can be snorted, injected and even smoked in some forms of the drug. In all cases cocaine is a strong central nervous system stimulant which affects the brain's processing of dopamine.

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Short-Term Effects

When cocaine is used it interferes with the reabsorption of dopamine, a brain chemical associated with pleasure and movement, producing a euphoric effect.

Shortly after cocaine is ingested the user may experience the following symptoms:

• Constricted blood vessels.
  
• Dilated pupils.
  
• Increased body temperature.
  
• Increased heart rate.
  
• Higher blood pressure.

During the euphoric period after cocaine use, which can last up until 30 minutes, user will experience hyperstimulation, reduced fatigue, and mental alertness. However, some users also experience restlessness, irritability, and anxiety.
During a cocaine binge, when the drug is taken repeatedly, users may experience increasing restlessness, irritability and paranoia. For some users this can lead to a period of paranoid psychosis, with auditory hallucinations and a disconnection with reality.

Long-Term Effects

Repeated cocaine use can cause the following health consequences:

• Irregular heart beat.
  
• Heart attack.
  
• Chest pain.
  
• Respiratory failure.
  
• Stroke.
  
• Seizures and headaches.
  
• Abdominal pain and nausea.

Chronic users of cocaine can become malnourished due to the drug's ability to decrease appetite. Each method of taking cocaine can produce specific health effects, including:

• Snorting: Chronically runny nose, nosebleeds, loss of smell, hoarseness, and problems swallowing.

• Ingesting: Severe bowel gangrene due to a reduction in the flow of blood to the intestines.
• Injecting: Severe allergic reactions. Increased risk for contracting HIV, Hepatitis and other blood-borne diseases.

See also other effects of long-term cocaine use.

Overdose

Although cocaine overdose is not common, it can occur and can be fatal. Because cocaine affects the heart and respiratory system, an overdose can cause death, especially when the drug is injected or smoked.
An overdose of cocaine can lead to:

• Irregular heart beat or heart failure.
  
• High blood pressure resulting in a brain hemorrhage.
  
• Repeated convulsions.
  
• Respiratory failure.

Addiction

Cocaine is highly addictive and those who smoke cocaine appear to develop an addiction to the drug more rapidly that those who snort it. However, even those who snort cocaine can find themselves addicted.
Cocaine users report that they are never able to achieve the "high" they felt the first time that they used the drug. A tolerance to the drug is developed so that the euphoric feeling users get is not as intense nor does it last as long.

When cocaine is injected, the euphoric feeling can last from 15 to 30 minutes, but when it is smoked, in may last only five to 10 minutes, causing the user to use more cocaine more often to try to maintain that high.

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Withdrawal

When cocaine users stop using cocaine, or when they end a cocaine binge, they immediately experience a "crash" which includes depression, fatigue, lack of pleasure, anxiety, irritability, sleepiness and a strong craving for more cocaine.
Some people experience agitation and extreme suspicion when they quit using cocaine, but cocaine withdrawal usually does not have visible physical symptoms like vomiting, chills and tremors that occur with the withdrawal of other drugs.

For those trying to quit a cocaine addiction, there are specific medical treatments available to help reduce withdrawal symptoms from professional rehabilitation facilities that specialize in the treatment of addiction.

See Also: The Health Effects of Other Drugs

Sources:
MedlinePlus
Office of National Drug Control Policy
National Institute on Drug Abuse