Drugs, Brains, and Behavior: The Science of Addiction
Addiction and Health

What are the other health consequences of drug addiction?

People with addiction often have one or more associated health issues, which could include lung or heart disease, stroke, cancer, or mental health conditions. Imaging scans, chest X-rays, and blood tests can show the damaging effects of long-term drug use throughout the body.

For example, it is now well-known that tobacco smoke can cause many cancers, methamphetamine can cause severe dental problems, known as meth mouth, and that opioids can lead to overdose and death. In addition, some drugs, such as inhalants, may damage or destroy nerve cells, either in the brain or the peripheral nervous system (the nervous system outside the brain and spinal cord).

Drug use can also increase the risk of contracting infections. HIV and hepatitis C (a serious liver disease) can occur from sharing injection equipment or from unsafe practices such as condom-less sex. 40,41 Infection of the heart and its valves (endocarditis) and skin infection (cellulitis) can occur after exposure to bacteria by injection drug use. 42

Does drug use cause other mental disorders, or vice versa?

Drug use and other mental illness often co-exist. In some cases, mental disorders such as anxiety, depression, or schizophrenia may come before addiction. In other cases, drug use may trigger or worsen those mental health conditions, particularly in people with specific vulnerabilities. 43,44

Some people with disorders like anxiety or depression may use drugs in an attempt to alleviate psychiatric symptoms. This may exacerbate their mental disorder in the long run, as well as increase the risk of developing addiction. 43,44 Treatment for all conditions should happen concurrently.

How can addiction harm other people?

The Impact of Addiction Can Be Far-Reaching

• Cardiovascular disease
• Stroke
• Cancer
• HIV/AIDS
• Hepatitis B and C
• Lung disease
• Mental disorders

Beyond the harmful consequences for the person with the addiction, drug use can cause serious health problems for others. Some of the more severe consequences of addiction are:

• Negative effects of drug use while pregnant or breastfeeding: A mother's substance or medication use during pregnancy can cause her baby to go into withdrawal after it's born, which is called neonatal abstinence syndrome (NAS). Symptoms will differ depending on the substance used, but may include tremors, problems with sleeping and feeding, and even seizures. 45 Some drug-exposed children will have developmental problems with behavior, attention, and thinking. Ongoing research is exploring if these effects on the brain and behavior extend into the teen years, causing continued developmental problems. In addition, some substances can make their way into a mother's breast milk. Scientists are still learning about long-term effects on a child who is exposed to drugs through breastfeeding.

• Negative effects of secondhand smoke: Secondhand tobacco smoke exposes bystanders to at least 250 chemicals that are known to be harmful, particularly to children. 46 Involuntary exposure to secondhand smoke increases the risks of heart disease and lung cancer in people who have never smoked. 5 Additionally, the known health risks of secondhand exposure to tobacco smoke raise questions about whether secondhand exposure to marijuana smoke poses similar risks. At this point, little research on this question has been conducted. However, a study found that some nonsmoking participants exposed for an hour to high-THC marijuana in an unventilated room reported mild effects of the drug, and another study showed positive urine tests in the hours directly following exposure. 47,48 If you inhale secondhand marijuana smoke, it's unlikely you would fail a drug test, but it is possible.
  
• Increased spread of infectious diseases: Injection of drugs accounts for 1 in 10 of cases of HIV. Injection drug use is also a major factor in the spread of hepatitis C, 49 and can be the cause of endocarditis and cellulitis. Injection drug use is not the only way that drug use contributes to the spread of infectious diseases. Drugs that are misused can cause intoxication, which hinders judgment and increases the chance of risky sexual behaviors, such as condom-less sex.

• Increased risk of motor vehicle accidents: Use of illicit drugs or misuse of prescription drugs can make driving a car unsafe—just like driving after drinking alcohol. Drugged driving puts the driver, passengers, and others who share the road at risk. In 2016, almost 12 million people ages 16 or older reported driving under the influence of illicit drugs, including marijuana. 50 After alcohol, marijuana is the drug most often linked to impaired driving. Research studies have shown negative effects of marijuana on drivers, including an increase in lane weaving, poor reaction time, and altered attention to the road.