A realistic concern for recreational users of marijuana is whether or not they will become addicted. There are no easy answers to this question. In my opinion, the most unbiased book on this and other related topics is The Science of Marijuana (2008). The Science of Marijuana is written by Leslie L. Iverson, a professor of pharmacology at the University of Cambridge in England. In the book, he reviews decades of international research on marijuana, both laboratory research and survey research. Based on his review of the scientific literature, between 10 to 30% of regular users will develop dependency. Only about 9% will have a serious addiction. For an excellent post on the biology of marijuana addiction see http://www.psychologytoday.com/blog/all-about-addiction/201001/is-marijuana-addictive-you-can-bet-your-heroin
The large majority of people who try marijuana do it experimentally and never become addicted. Unlike other substances, pot has very few severe withdrawal symptoms and most people can quit rather easily. When present, withdrawal symptoms might include: anxiety, depression, nausea, sleep disturbances and GI problems.
Compared to other substances, marijuana is not very addicting. It is estimated that 32% of tobacco users will become addicted, 23% of heroin users, 17% of cocaine users, and 15% of alcohol users. Cocaine and heroin are more physically harmful and nicotine is much more addictive. It is much harder to quit smoking cigarettes than it is to quit smoking pot.
Recreational users of the past are often compared to todays smokers. The smokers, the times and the pot are all different. According to Iversen, marijuana became widely used in the US during the 1960s by Vietnam vets. This was a time of social upheaval and strong anti-war sentiment. Youth were rebellious and experimental pot smokers. Today's youth are different. They are mainstream. Interestingly, many of today's young smokers are children of the previous generation of smokers. And, my generation of marijuana smokers quit relatively easily when they became parents and homeowners.
It is often said that today's pot is stronger. I am not sure how anybody could know this. Readers, if you know please tell me. Are there studies comparing THC content of 1970 pot with 2010 pot? How could this even be possible on a large scale? Does somebody still have some 1970 pot sitting around or are we relying on old memories? The only thing that I can surmise is that the marijuana that is carefully cultivated indoors these days is more potent than previous strains. In fact, this brings to mind one of my greatest frustrations. In California, small amounts of marijuana are legal for people with 215 cards but it is not regulated. So, how does anybody know how much THC they are smoking? Do they even know where it was grown and how much pesticide it contains? For example, when I buy Advil in the supermarket, I know that I am getting 200 mg capsules.
In spite of different strains of marijuana containing different amounts of THC, experienced smokers are able to control their high. An interesting study reported in Iversen's book claims that regular users know how to inhale in a way that regulates THC content. A study was conducted where experienced smokers were given joints with either 1% or 4% levels of THC. The subjects were blind to experimental conditions so they didn't know the THC content of the joint. Without knowing which joint they were smoking, the smokers automatically adjusted their inhaling to reach about the same degree of high and THC absorption. They did this by taking longer and harder draws on the weaker joint and breathing in more air with the more potent joint.
So, to wrap up, is marijuana addictive? For most people, no. About 10% of recreational users will develop problems serve enough to impair their work and relationships. Many more will come to depend on pot for relaxation and social purposes. This will be problematic if they don't learn more effective coping mechanisms and come to rely on marijuana instead of solving their problems. When ready, most people will be able to quit with only mild withdrawal symptoms. And, compared to other recreational drugs, marijuana is relatively harmless. But, it is not completely harmless. And...what is more serious than its addictive consequences are the legal ones. This relatively harmless herbal plant is unregulated and illegal in the U.S.