This article includes links to many research studies, some linked to below, for the rest go to the full article.
Most People With Addiction Simply Grow Out of It by Maia Szalavitz
By age 35, half of all people who qualified for active alcoholism or addiction diagnoses during their teens and 20s no longer do.
The average cocaine addiction lasts four years, the average marijuana addiction lasts six years, and the average alcohol addiction is resolved within 15 years. Heroin addictions tend to last as long as alcoholism, but prescription opioid problems, on average, last five years. In these large samples, which are drawn from the general population, only a quarter of people who recover have ever sought assistance in doing so (including via 12-step programs). This actually makes addictions the psychiatric disorder with the highest odds of recovery.
If you start drinking or taking drugs with peers before age 18, you have a 25% chance of becoming addicted, but if your use starts later, the odds drop to 4%. Very few people without a prior history of addiction get hooked later in life, even if they are exposed to drugs like opioid painkillers.
These results can give people hope when they, or loved ones, are suffering from an addiction. Treatment helps sometimes but also fails quite often. Even in the case where things are not looking good, there is hope that eventually things may run there course.
Of course, there is a risk, sadly, that before the addiction ends tragedy will strike. So hopefully we can keep researching methods to better treat addiction. But if things are failing (especially for one you love) there may be light at the end of the dark tunnel.