It depends on the drug, but all drugs can cause negative health effects and can lead to addiction.
Addiction is defined as a chronic, relapsing brain disease that is characterized by compulsive drug seeking and use, despite harmful consequences. It is considered a brain disease because drugs change the brain—they change its structure and how it works. These brain changes can be long lasting, and can lead to the harmful behaviors seen in people who abuse drugs.1
Individuals who suffer from addiction often have one or more accompanying medical issues, including lung and cardiovascular disease, stroke, cancer, mental disorders, and obesity; and drug use can also make them susceptible to contracting HIV, hepatitis, and other diseases. Imaging scans, chest x-rays, and blood tests show the damaging effects of drug abuse throughout the body. In addition, some drugs are toxic to nerve cells and may damage or destroy them either in the brain or the peripheral nervous system.2
Some of these effects occur when drugs are used at high doses or for prolonged periods of time. However, some may occur after just one use.
In addition to health effects like those described above, drugs can also have negative social consequences that can really hurt people—being unreliable, forgetting things, telling lies, stealing money for drugs, sometimes even getting violent with people they love. Their biggest ambition becomes getting high.
While addiction may result from any drug use, there are unique health effects for each drug.
NIDA Medical Consequences of Drug Abuse
Published 2007. View Source
National Institute on Drug Abuse The Brain: Understanding Neurobiology Through the Study of Addiction
Bethesda, MD: NIDA, NIH, DHHS. Retrieved June 2003. View Source