Commonly-cited arguments for and against the prohibition of drugs include the following:

Efficiency

Arguments that drug laws are effective

Supporters of prohibition claim that drug laws have a successful track record suppressing illicit drug use since they were introduced in the 1910s. The licit drug alcohol has current (last 12 months) user rates as high as 80–90% in populations over 14 years of age, and tobacco has historically had current use rates up to 60% of adult populations, yet the percentages currently using illicit drugs in OECD countries are generally below 1% of the population excepting cannabis where most are between 3% and 10%, with six countries between 11% and 17%.

In the 50-year period following the first 1912 international convention restricting use of opium, heroin and cocaine, the United States' use of illicit drugs other than cannabis was consistently below 0.5% of the population, with cannabis rising to 1–2% of the population between 1955 and 1965. With the advent of the counter-culture movement from the late 1950s, where illicit drug use was promoted as mind-expanding and relatively harmless, illicit drug use rose sharply. With illicit drug use peaking in the 1970s in the United States, the "Just Say No" campaign, initiated under the patronage of Nancy Reagan, coincided with recent (past month) illicit drug use decreases from 14.1% in 1979 to 5.8% in 1992, a drop of 60%.

In March, 2007, Antonio Maria Costa, former executive director of the United Nations Office on Drugs and Crime, drew attention to the drug policy of Sweden, arguing:

In Europe as of 2007, Sweden spends the second highest percentage of GDP, after the Netherlands, on drug control. The UNODC argues that when Sweden reduced spending on education and rehabilitation in the 1990s in a context of higher youth unemployment and declining GDP growth, illicit drug use rose but restoring expenditure from 2002 again sharply decreased drug use as student surveys indicate.

Criticizing governments that have relaxed their drug laws, Antonio Maria Costa, speaking in Washington before the launch of the World Drug Report in June 2006, said:

Arguments that drug laws are ineffective

One of the prominent early critics of prohibition in the United States was August Vollmer, founder of the School of Criminology at University of California, Irvine and former president of the International Association of Chiefs of Police. In his 1936 book The Police and Modern Society, he stated his opinion that:

Stephen Rolles, writing in the British Medical Journal in 2010, argues:

These conclusions have been reached by a succession of committees and reports including, in the United Kingdom alone, the Police Foundation, the Home Affairs Select Committee, the Prime Minister's Strategy Unit, the Royal Society of Arts, and the UK Drug Policy Consortium. The United Nations Office of Drugs and Crime has also acknowledged the many "unintended negative consequences" of drug enforcement.

The editor of the British Medical Journal, Dr. Fiona Godlee, gave her personal support to Rolles' call for decriminalisation, and the arguments drew particular support from Sir Ian Gilmore, former president of the Royal College of Physicians, who said we should be treating drugs "as a health issue rather than criminalising people" and "this could drastically reduce crime and improve health".

Danny Kushlik, head of external affairs at Transform, said the intervention of senior medical professionals was significant. He said: "Sir Ian's statement is yet another nail in prohibition's coffin. The Hippocratic oath says: 'First, do no harm'. Physicians are duty bound to speak out if the outcomes show that prohibition causes more harm than it reduces."

Nicholas Green, chairman of the Bar Council, made comments in a report in the profession's magazine, in which he said that drug-related crime costs the UK economy about £13bn a year and that there was growing evidence that decriminalisation could free up police resources, reduce crime and recidivism and improve public health.

A 2006 report sponsored by the New York County Lawyers' Association, one of the largest local bar associations in the United States, argues on the subject of US drug policy:

In response to claims that prohibition can work, as argued by Antonio Maria Costa, executive director of the United Nations Office on Drugs and Crime, who drew attention to the drug policy of Sweden, Henrik Tham has written in 1998 that sometimes it's domestically important to stress drug policy as successful; in the case of Sweden, where this notion is important, such claims serve "the function of strengthening a threatened national identity in a situation where the traditional 'Swedish model' has come under increasingly hard attack from both inside and outside the country." Tham questions the success of the Swedish model – "The shift in Swedish drug policy since around 1980" ...(more difficult to receive nolle prosequi for minor drug crimes)

Leif Lenke and Börje Olsson from Stockholm University have conducted research that showed how drug use have followed the youth unemployment in close correlation. They noted that unlike most of Europe, Sweden did not have widespread and lingering youth unemployment until the early 1990s financial crisis, suggesting that unattractive future prospects may contribute to the increase in drug use among the young. CAN, the Swedish Council for Information on Alcohol and Other Drugs, 2009 report stated that the increase in drug use have continued since the 1990s with a slight dip in the mid-2000.

The professor emeritus in criminology at the University of Oslo, Nils Christie, pointed out Sweden as the hawk of international drug policy in a 2004 book. He said that Sweden is serving the role of being welfare alibi for, and lending legitimacy to, the US drug war. Adding that USA and Sweden have had an extraordinary influence on UNODC as the biggest donor countries. Sweden was the second biggest donor financing 8% of the UNODC budget behind the European Commission in 2006, followed by the US. In 2007 and 2008 Sweden was the fourth biggest donor, behind the European Commission, USA and Canada. In 2009 it was the third, as USA withdrew some of its funding.

A 2009 editorial in The Economist argued:

Antonio Maria Costa's conviction that "countries have the drug problem they deserve" if they fail to follow the "Swedish Model" in drug control has also been criticised in Peter Cohen's work – Looking at the UN, smelling a rat.

In its 2011 report, the Global Commission on Drug Policy stated that "The global war on drugs has failed, with devastating consequences for individuals and societies around the world".

Deterrence

Arguments that prohibition discourages drug use

A 2001 Australian study, of 18- to 29-year-olds by the NSW Bureau of Crime Statistics and Research suggests that prohibition deters illicit drug use. 29% of those who had never used cannabis cited the illegality of the substance as their reason for never using the drug, while 19% of those who had ceased use of cannabis cited its illegality as their reason.

Gil Kerlikowske, director of the US ONDCP argued,

The DEA argues "Legalization has been tried before—and failed miserably. Alaska's experiment with legalization in the 1970s led to the state's teens using marijuana at more than twice the rate of other youths nationally. This led Alaska's residents to vote to re-criminalize marijuana in 1990."

Drug Free Australia has cited the Netherlands as an example of drug policy failure because it is soft in approach. They argue that the Dutch idea of going soft on cannabis dealers, thereby creating a "separation of markets" from hard drug dealers has failed to stem the initiation to drugs such as heroin, cocaine, and amphetamines, saying that, in 1998, the Netherlands had the third highest cannabis and cocaine use in Europe. Gil Kerlikowske has attested that, where there were once thousands of cannabis cafés there are now only several hundred. Levels of cannabis use, in 2005 only marginally higher than in 1998, while other European countries have accelerated past them, are more likely, Drug Free Australia argues, the result of a growing intolerance of cannabis in the Netherlands rather than a growing tolerance.

Arguments that prohibition does not discourage drug use

It has been suggested that drug law reform could reduce the use of hard drugs as it has in countries such as the Netherlands. According to a 2009 annual report by the European Monitoring Centre for Drugs and Drug Addiction, the Dutch are among the lowest users of marijuana or cannabis in Europe, despite the Netherlands' policy on soft drugs being one of the most liberal in Europe, allowing for the sale of marijuana at "coffee shops", which the Dutch have allowed to operate for decades, and possession of less than .

British Crime Survey statistics indicated that the proportion of 16- to 24-year-olds using cannabis decreased from 28% a decade ago to 21%, with its declining popularity accelerating after the decision to downgrade the drug to class C was announced in January 2004. The BCS figures, published in October 2007, showed that the proportion of frequent users in the 16–24 age group (i.e. who were using cannabis more than once a month), fell from 12% to 8% in the past four years.

American teenagers are drinking and smoking less and doing fewer drugs than their predecessors in more than 40 years of tracking. Use of marijuana is down among 8th- and 10th-graders, though it is flat among high school seniors, according to the annual Monitoring the Future survey of American teens.

A 2008 scholarly study found that intensified enforcement of marijuana laws does not achieve the stated goals of

marijuana prohibition and that "decriminalizing marijuana possession or deprioritizing marijuana law enforcement does not appear to increase marijuana use".

Gateway drug theory

Arguments that cannabis is a gateway drug

The US Drug Enforcement Agency's "2008 Marijuana Sourcebook" argues that recent research supports the gateway hypothesis that certain drugs (such as cannabis) act as gateways to use of 'harder' drugs such as heroin, either because of social contact or because of an increasing search for a better high. Proponents cite studies such as that of 311 same sex twins, where only one twin smoked cannabis before age 17, and where such early cannabis smokers were five times more likely than their twin to move on to harder drugs.

Arguments that cannabis is not a gateway drug

In the American Journal of Public Health, Andrew Golub and Bruce Johnson of the National Development and Research Institute in New York wrote that young people who smoked marijuana in the generations before and after the baby boomers did not appear to be likely to move on to harder drugs.

Researchers from the independent Rand Drug Policy Research Center in Santa Monica, California, looking at data from the National Household Survey on Drug Abuse between 1982 and 1994, concluded that teenagers who took hard drugs did so whether they had first tried cannabis or not.

A twin study (of 510 same sex twin pairs) which adjusted for additional confounders such as peer drug use, found that cannabis use and associations with later hard drug use existed only for non-identical twins. The study suggested that a causal role of cannabis use in later hard drug usage is minimal, if it exists at all, and that cannabis use and hard drug use share the same influencing factors such as genetics and environment.

Health

Health arguments for drug laws

Advocates of prohibition argue that particular drugs should be illegal because they are harmful. Drug Free Australia for example argues "That illicit drugs are inherently harmful substances is attested by the very nomenclature of the 'harm reduction' movement." Ratios of the harms of illicit opiates to licit alcohol and tobacco in Australia are similar, with 2 deaths per hundred opiate users per annum versus 0.22 deaths per hundred for alcohol (9 times less) per year and 0.3 for tobacco (7 times less). are more likely to figure in the longer term, just as with tobacco, where both nicotine overdose and cannabis overdose are extremely rare or nonexistent. While ecstasy may have lower rates of immediate mortality than some other illicits, there is a growing science on the already recognized considerable health harms of ecstasy. Drug Free Australia argues that distinctions between "soft" and "hard" drugs are entirely artificial, and titling cannabis "soft" or ecstasy "recreational" does not lessen the extensive harms of these substances.

Drug Free Australia claims arguments that increased health harms of illicit drugs are the result of lack of government regulation of their purity and strength are not well supported by evidence. In Australia, which has had the highest opioid mortality per capita in the OECD, Drug Free Australia claims that other causes of death such as suicide, murder and accidents are an effect of the drug themselves, not of their purity or otherwise. ]]

There is evidence that some illicit drugs pose comparatively fewer health dangers than certain legal drugs. the risks from cannabis use also overstated, and health problems from the use of legal substances, particularly alcohol and tobacco, are greater, even than from cocaine use for example (occasional cocaine use does not typically lead to severe or even minor physical or social problems).

Health benefits

A 2015 study of 135,095 U.S. adults found no significant link between lifetime psychedelic use and increased mental health problems or suicidal behavior. The researchers concluded that the prohibition of psychedelics is challenging to justify on public health grounds, given these findings.

Many trials have shown beneficial effects associated with psychoactive drug use:

  • There is evidence that MDMA (ecstasy) can treat or cure post-traumatic stress disorder and anxiety in cases of terminal illness.
  • LSD has been widely researched as a therapeutic agent, and has shown effectiveness against alcoholism, frigidity and various other disorders. See Psychedelic therapy.
  • Researchers at Harvard-affiliated McLean Hospital found members of a religious group regularly using peyote scored significantly better on several measures of overall mental health than did subjects who did not use the hallucinogen.
  • A 2007 study, by Santos et al. found that users of ayahuasca scored better on tests measuring anxiety and hopelessness than people who did not use the drug.

Quality control

According to a World Health Organization report: "As cannabis is an illegal drug its cultivation, harvesting and distribution are not subject to quality control mechanisms to ensure the reliability and safety of the product used by consumers. It is well recognised in developing countries, such as Kenya, that illicit alcohol production can result in the contamination with toxic by-products or adulterants that can kill or seriously affect the health of users. The same may be true of illicit drugs such as opiates, cocaine and amphetamine in developed societies."

The government cannot enforce quality control on products sold and manufactured illegally. Examples include: the easier to make derivative MDA being sold as MDMA, heroin users unintentionally injecting brick dust, quinine, or fentanyl with which their heroin had been cut; and heroin/cocaine overdoses occurring as a result of users not knowing exactly how much they are taking. If the supply of drugs such as ecstasy came from legitimate pharmaceutical companies, their product would be far less likely to contain toxic additives or varying dosages. This is a view supported by a number of parents whose children have died of overdoses.

The illegality of injectable drugs leads to a scarcity of needles which causes an increase in HIV infections. An easy cure to this problem, while upholding the illegality of drugs, is the Dutch policy of distributing free needles. The money spent on both increased health costs due to HIV infections and drug prohibition itself causes a drain upon society.

Studies on the effects of prescribing heroin to addicts as practiced in many European countries have shown better rates of success than any other available treatment in terms of assisting long-term users establish stable, crime-free lives. Many patients were able to find employment, some even started a family after years of homelessness and delinquency.

Block to research

The illegality of many recreational drugs may be dissuading research into new, more effective and perhaps safer recreational drugs, despite evidence that their use may be beneficial in certain contexts. Research on Schedule I drugs in many countries, including the United States and United Kingdom, and under international law, is tightly regulated and requires expensive and hard-to-obtain permits. Such restrictions have largely prevented investigation of their properties and therapeutic uses, and most research since the passage of the drug laws focuses on negative impacts of these drugs. For example, all known agonists of the 5HT<sub>2A</sub> receptor are psychedelics, which prevents research into this receptor.

In particular, research suggests that recreational drugs may have psychiatric applications, which many demonstrating potential for treatment-resistant mental health conditions, such as depression and anxiety. Those who support the legalisation of recreational drugs for research purposes highlight that it is unethical not to conduct research into therapeutic interventions that may have the potential to treat these conditions.

Misleading health statistics

The United States Drug Enforcement Administration (DEA) has suggested that illegal drugs are "far more deadly than alcohol", arguing that "although alcohol is used by seven times as many people as drugs, the number of deaths induced by those substances is not far apart", quoting figures from the Centers for Disease Control and Prevention (CDC), claiming "during 2000, there were 15,852 drug-induced deaths; only slightly less than the 18,539 alcohol-induced deaths." The DEA's argument also overlooks tobacco, causing 435,000 US deaths in year 2000. and deaths from medically prescribed (not illegal) drugs. An analysis of drug-induced deaths for the 20-year period 1979–1998 found the vast majority attributable to accidental overdose, and suicide by drug taking, which together account for about 76 percent of all such deaths. Taking into account deaths from non-illegal drugs leaves only 21 percent of CDC "drug-induced death" figures actually due to the use of "illegal" drugs.

Claims that cannabis is far more powerful than it used to be are also dubious, with "scare figures" skewed by comparing the weakest cannabis from the past with the strongest of today. Figures regarding emergency room mentions of marijuana use can be misleading too, as "mention" of a drug in an emergency department visit does not mean that the drug was the cause of the visit.

Medical uses

A document published for the non-profit advocacy organization Europe Against Drugs (EURAD) argues that "one cannot vote for a medicine" and that a scientific approval basis is essential. It says that EU rules set out strict criteria for the acceptance of a drug for medical use:

Arguments against medical uses of prohibited drugs

According to Janet D. Lapey, M.D., of Concerned Citizens For Drug Prevention, " Due to a placebo effect, a patient may erroneously believe a drug is helpful when it is not. This is especially true of addictive, mind-altering drugs like marijuana. A marijuana withdrawal syndrome occurs, consisting of anxiety, depression, sleep and appetite disturbances, irritability, tremors, diaphoresis, nausea, muscle convulsions, and restlessness. Often, persons using marijuana erroneously believe that the drug is helping them combat these symptoms without realizing that actually marijuana is the cause of these effects. Therefore, when a patient anecdotally reports a drug to have medicinal value, this must be followed by objective scientific studies."

The US Drug Enforcement Administration also says: