How much cocaine is used daily by an addict?

It depends on numerous factors, including how you define "addicted". A person may be physically dependent or psychologically dependent on a drug. An example of physical dependence is a heroin addict who has loose stools, cold sweats, hot flashes, body aches, nausea and other symptoms when heroin use is ceased. An example of psychological dependence is when a cocaine addict feels bored, like he has a void in his life, when he ceases cocaine use.

The length of time varies between substances and individuals. Some people use drugs all of their lives and never become addicted. Others use drugs only for a short period of time and become addicted. Explaining this answer in full detail would result in me writing a book-sized post, so I will give a brief overview of a few highly addicted drugs.

Heroin: Users typically become addicted after 5 days to 2 weeks of heavy daily use.

Benzodiazepines (Xanax, Klonopin, Valium, etc): Users typically become addicted after at least one month of daily use.

Marijuana: Research is mixed on whether individuals actually become physically dependent on marijuana, with new research supporting that physical dependence occurs but does not present itself due to the long half-life of marijuana. Users typically develop some type of dependence for marijuana after near daily use for multiple months in a row.