Concept:Drug abuse is the harmful use of substances that affect the brain and behaviour.
It most often results in mental or psychiatric problems.
Explanation:Drug abuse changes the way the brain works.
It can cause confusion, mood swings, depression, and hallucinations.
These conditions are known as psychiatric disorders.
The other options, such as sexually transmitted disease, cancerous illness, and incurable ailment, are not the direct or most common effects of drug abuse.
Answer:C. psychiatric disorder