Students who were banned from smoking legal cannabis in Dutch coffeeshops were found to be more likely to pass exams, specifically maths-based ones, according to researchers. 
 
 The findings were worked out during a temporary “partial-prohibition” of cannabis cafes in the city of Maastricht, in which people were not allowed to enter on the sole basis of their nationalities. 
 
 Students who were banned from the 13 coffee shops in the city have been 5.4 per cent more likely to pass their courses, economists at the University of Maastricht found. 
 
 The effect is “five times larger” for courses requiring quantitative thinking and maths-based tasks, the researchers wrote. 
 
 Lower performers – who had a pre-study GPA below the median of 6.62 – were most impacted by the ban with a 7.6 per cent increase in probability of passing a course. This may be down to ‘high’ achievers already getting top grades, regardless of cannabis consumption, they added. 
 
 Where cannabis is and isn't legal 
 
 
 
 
 
 
 
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 1/12 UK Having been reclassified in 2009 from a Class C to a Class B drug, cannabis is now the most used illegal drug within the United Kingdom. The UK is also, however, the only country where Sativex – a prescribed drug that helps to combat muscle spasms in multiple sclerosis and contains some ingredients that are also found in cannabis - is licensed as a treatment Getty 
 
 2/12 North Korea Although many people believe the consumption of cannabis in North Korea to be legal, the official law regarding the drug has never been made entirely clear whilst under Kim Jong Un’s regime. However, it is said that the North Korean leader himself has openly said that he does not consider cannabis to be a drug and his regime doesn’t take any issue with the consumption or sale of the drug MARCEL VAN HOORN/AFP/Getty Images 
 
 3/12 Netherlands In the Netherlands smoking cannabis is legal, given that it is smoked within the designated ‘smoking areas’ and you don’t possess more than 5 grams for personal use. It is also legal to sell the substance, but only in specified coffee shops Getty 
 
 4/12 USA Although in some states of America cannabis has now been legalised, prior to the legalisation, police in the U.S. could make a marijuana-related arrest every 42 seconds, according to US News and World Report. The country also used to spend around $3.6 billion a year enforcing marijuana law, the American Civil Liberties Union notes AP Photo/Ted S. Warren 
 
 5/12 Spain Despite cannabis being officially illegal in Spain, the European hotspot has recently started to be branded, ‘the new Amsterdam’. This is because across Spain there are over 700 ‘Cannabis Clubs’ – these are considered legal venues to consume cannabis in because the consumption of the drug is in private, and not in public. These figures have risen dramatically in the last three years – in 2010 there were just 40 Cannabis Clubs in the whole of Spain. Recent figures also show that in Catalonia alone there are 165,000 registered members of cannabis clubs – this amounts to over 5 million euros (£4 million) in revenue each month Getty 
 
 6/12 Uruguay In December 2013, the House of Representatives and Senate passed a bill legalizing and regulating the production and sale of the drug. But the president has since postponed the legalization of cannabis until to 2015 and when it is made legal, it will be the authorities who will grow the cannabis that can be sold legally. Buyers must be 18 or older, residents of Uruguay, and must register with the authorities Getty 
 
 7/12 Pakistan Despite the fact that laws prohibiting the sale and misuse of cannabis exist and is considered a habit only entertained by lower-income groups, it is very rarely enforced. The occasional use of cannabis in community gatherings is broadly tolerated as a centuries old custom. The open use of cannabis by Sufis and Hindus as a means to induce euphoria has never been challenged by the state. Further, large tracts of cannabis grow unchecked in the wild Getty 
 
 8/12 Portugal In 2001, Portugal became the first country in the world to decriminalize the use of all drugs, and started treating drug users as sick people, instead of criminals. However, you can still be arrested or assigned mandatory rehab if you are caught several times in possession of drugs Getty 
 
 9/12 Puerto Rico Although the use of cannabis is currently illegal, it is said that Puerto Rico are in the process of decriminalising it RAUL ARBOLEDA/AFP/Getty Images 
 
 10/12 Colorado The US state became the first in the country to legalise marijuana in January 2014. In February 2015, President Obama recently said he expects to see more states "looking into" legalisation. However, it is illegally to grow more than six cannabis plants and to possess more than 28 grams of the drug Rex Features 
 
 11/12 California Oaksterdam in Oakland, California, is the world's only university dedicated to the study and cultivation of cannabis. If you are court in California with anything up to an ounce of cannabis, you will be fine $100, but you will not get a criminal record, nor will you have to appear in court Getty Images 
 
 12/12 China Cannabis is grown in the wild and has been used to treat conditions such as gout and malaria. But, officially the substance is illegal to consume, possess and sell Getty 
 
 The study comes after 20 US states legalised the use of medicinal cannabis and 14 others took some steps to decriminalise possession. Uruguay is planning to become the first nation in the world to fully legalise all aspects of the cannabis trade. 
 
 Women were also found to have higher improved grades than men, which researchers Olivier Marie and Ulf Zölitz believe is down to differences in processing high amounts of THC found in Dutch weed, which is often twice as strong as that in the US. 
 
 They also claim that grade improvements are not in correlation with any increases in effort or amount of study hours. The undergraduates have a median age of 20.6, and most of the improvements were also found in those who were the youngest. 
 
 A legal cannabis dispensary in the US state of Colorado 
 
 Online evaluations filled in by the students showed that overall understanding of their courses improved the most when they did not smoke in coffeeshops. 
 
 “The effects we find are large, consistent and statistically very significant,” Marie told the Observer. “For example, we estimate that students who were no longer able to buy cannabis legally were 5% more likely to pass courses. 
 
 “The grade improvement this represents is about the same as having a qualified teacher and, more relevantly, similar to decreases in grades observed from reaching legal drinking age in the US.” 
 
 The seven-month policy implemented by the Maastricht association of cannabis-shop owners (VOCM) from October 2011, after pressure by local authorities, had sought to control weed smoking by “drug tourists” from neighbouring countries. 
 
 Coffeeshops are found in major Dutch cities like Amsterdam 
 
 People from France and Luxembourg were found to be the “bad tourists,” according to the study, as they had been “creating the most nuisance” for the city’s residents. 
 
 Belgian and German citizens were allowed to use cannabis cafes and, including Dutch people, they comprise 90 per cent of all customers – which shows that the “partial prohibition” was only carried out on a minority of people. 
 
 Researchers admit that students who were banned could have got hold of cannabis illegally through friends and dealers, however they believe that the findings are significant enough to be considered when international drug laws are amended. 
 
 More than 54,000 grades were analysed of around 4,200 students. Fifty-two per cent were German, 33 per cent Dutch, six per cent Belgian and remaining eight per cent listed as “other”. ||||| If you want to do well in your exams, especially maths, don’t smoke dope. 
 
 This is the finding of a unique study that is likely to be fiercely debated by those in favour of and those against the liberalisation of cannabis laws. Economists Olivier Marie of Maastricht University and Ulf Zölitz of IZA Bonn examined what happened in Maastricht in 2011 when the Dutch city allowed only Dutch, German and Belgian passport-holders access to the 13 coffee shops where cannabis was sold. The temporary restrictions were introduced because of fears that nationals from other countries, chiefly France and Luxembourg, were visiting the city simply to smoke drugs, which would tarnish its genteel image. 
 
 After studying data on more than 54,000 course grades achieved by students from around the world who were enrolled at Maastricht University before and after the restrictions were introduced, the economists came to a striking conclusion. In a paper recently presented at the Royal Economic Society conference in Manchester they revealed that those who could no longer legally buy cannabis did better in their studies. The restrictions, the economists conclude, constrained consumption for some users, whose cognitive functioning improved as a result. 
 
 “The effects we find are large, consistent and statistically very significant,” Marie told the Observer. “For example, we estimate that students who were no longer able to buy cannabis legally were 5% more likely to pass courses. The grade improvement this represents is about the same as having a qualified teacher and, more relevantly, similar to decreases in grades observed from reaching legal drinking age in the US.” 
 
 For low performers, there was a larger effect on grades. They had a 7.6% better chance of passing their courses. 
 
 Interestingly, Marie and Zölitz found the effects were even more pronounced when it came to particular disciplines. “The policy effect is five times larger for courses requiring numerical/mathematical skills,” the pair write. 
 
 This, they argue, is not that surprising. “In line with how THC consumption affects cognitive functioning, we find that performance gains are larger for courses that require more numerical/mathematical skills,” Marie said. THC – tetrahydrocannabinol – is the active ingredient in skunk cannabis, which some studies have linked with psychosis. 
 
 The groundbreaking research comes at a significant moment. The clamour for liberalisation of cannabis laws is growing. In Germany, Berlin is considering opening the country’s first legal cannabis shop. Uruguay plans to be the first nation in the world to fully legalise all aspects of the cannabis trade. In the US, more than 20 states now allow medical marijuana use, while recreational consumption has become legal in Alaska, Oregon, Washington and Colorado. 
 
 But, as Marie and Zölitz observe in their paper: “With scarce empirical evidence on its societal impact, these policies are mainly being implemented without governments knowing about their potential impact. 
 
 “We think this newfound effect on productivity from a change in legal access to cannabis is not negligible and should be, at least in the short run, politically relevant for any societal drug legalisation and prohibition decision-making,” Marie said. “In the bigger picture, our findings also indicate that soft drug consumption behaviour is affected by their legal accessibility, which has not been causally demonstrated before.” 
 
 The research is likely to be seized upon by anti-legalisation campaigners. But Marie was at pains to say the research should simply be used to raise awareness of an often overlooked aspect of drug use: its impact on the individual’s cognitive ability. “If marijuana is legalised like it is in many states in the US, we should at least inform consumers about the negative consequences of their drug choices.” 
 
 It will also feed into the debate about THC levels in cannabis, which are becoming ever stronger. Levels of THC in marijuana sold in Maastricht’s coffee shops are around double those in the US. 
 
 “Considering the massive impact on cognitive performance high levels of THC have, I think it is reasonable to at least inform young users much more on consequences of consuming such products as compared with that of having a beer or pure vodka,” Marie said. 
 
 History suggests that prohibition often results in the illicit drug or alcohol trade producing ever stronger products. Campaigners for liberalisation argue that it could help bring THC levels down and allow users to know what they are buying. The authors concede that their findings could turn out to be different if they were to replicate their study in a country that did not have restrictions on cannabis use. 
 
 Marie said his work had helped inform his discussions with his teenage son. “I have a 13-year old boy and I do extensively share this with him as a precautionary measure so that he can make the best informed choice if he is faced with the decision of whether to consume cannabis or not.”
– Hanging out in marijuana cafes and smoking the night away is not exactly good for your grades, especially in math, according to a new study. Researchers drew this conclusion after comparing more than 54,000 grades of undergraduates in the Dutch city of Maastricht, where some were banned from the city's 13 cannabis coffee shops, the Guardian reports. The upshot: The banned students had a 5% better chance of passing courses. For weaker students, the improvement in their chances rose to 7.6%. And the overall effect was a stunning five times higher for courses involving numbers and math. "The effects we find are large, consistent, and statistically very significant," says study co-author Olivier Marie. "The grade improvement this represents is about the same as having a qualified teacher." Marie says it's hardly surprising, since we already know that THC (the main psychoactive ingredient in cannabis) affects cognitive functioning. But this comes at a key moment, as more than 20 states in the US permit weed for medical use, four states allow recreational use, and Uruguay may become the first country to totally legalize cannabis. The finding could also inform the debate over THC levels, which are getting higher. "I think it is reasonable to at least inform young users much more on consequences of consuming such products," says Marie. An amusing side note: The study says that students from France and Luxembourg had been banned from the cafes for being "drug tourists" and "creating the most nuisance" for locals, the Independent reports. (Read about a drug that could "top" medical marijuana.)