The medical journal Jama Internal Medicine has published a study on the effects of cannabis on human memory, and as expected the results show that the drug is dangerous. Scientists based their study on 3400 Americans over a 25-year period, who were given fifteen words to memorise. Those who smoked every day for five years remembered half a word less than those who did not smoke or who did but in moderation (8.5 words versus 9). This total rises to 2.5 words less after 25 years of smoking. However, it has been proven that marijuana use in no way affects your IQ, or your abilities of concentration and deduction. However, cannabis exposes you, among other things, to addiction and depression.