Disclaimer: The following information was sourced from our friends at Bud Buddies. I commend their hard work writing the following information and use it only for educational purposes. Available at ‘http://www.budbuddies.co.uk/10-cannabis-myths/

Cannabis is a dangerous drug and causes dependence

The definition of addiction is:
“A compulsive physiological and psychological need for a habit-forming substance”
It is possible to develop a psychological addiction to most things that are taken to excess, however cannabis is not physically addictive, although it is accepted that in some cases a psychological dependence can occur in heavy to chronic users.
According to the National Academy of Sciences’ Institute of Medicines report ‘Marijuana and Medicine: Assessing the Science Base’:
“Compared to most other drugs dependence among marijuana users is relatively rare, although few marijuana users develop dependence, some do. But they appear to be less likely to do so than users of other drugs (including alcohol and nicotine), and marijuana dependence appears to be less severe than dependence on other drugs.”
Even heavy cannabis consumers will not suffer withdrawal as is the case with alcohol, hard drugs and many prescription medicines. Some chronic users who stop using cannabis report experiencing irritability, restlessness and find it difficult to sleep for a short period after discontinuing use.
Numerous studies have concluded that cannabis is not physically addictive and the greatest danger to cannabis consumers is smoking cannabis mixed with tobacco.
This is a very interesting study:
“To determine the degree to which cigarette smoking predicts levels of cannabis dependence above and beyond cannabis use itself, concurrently and in an exploratory four-year follow-up, and to investigate whether cigarette smoking mediates the relationship between cannabis use and cannabis dependence”
Download the full report here: Associations between cigarette smoking and cannabis dependence: A longitudinal study of young cannabis users in the United Kingdom

Cannabis is a 'Gateway' drug

The argument that cannabis can be a ‘gateway’ drug (cannabis consumers will move onto harder drugs) is a common argument used by supporters of the prohibition of cannabis. However, many studies throughout the world report that if there is a link to cannabis and harder drugs that is due to the fact that cannabis is treated by many jurisdictions as an illicit drug and therefore the ‘dealer’ who supplies cannabis often has other ‘harder’ drugs available.
According to the National Academy of Sciences’ Institute of Medicines report ‘Marijuana and Medicine: Assessing the Science Base’:
“There is no conclusive evidence that the drug effects of marijuana are causally linked to the subsequent abuse of other illicit drugs. There is no evidence that marijuana serves as a stepping stone on the basis of its particular physiological effect.”
Cannabis is one of the safest medicines available. There has never been a single recorded fatality from cannabis in over 10,000 years of known human use. Despite scientific evidence that cannabis is very beneficial in treating many illnesses and diseases, in many countries cannabis is classed as a schedule one drug, deeming it to have “no medicinal value”.

Cannabis causes schizophrenia

Some studies have indicated that individuals who are predisposed to being sensitive to THC can experience a psychotic episode when exposed to very high THC levels (without CBD). However, people who are predisposed generally exhibit schizophrenic behaviour prior to any consumption of cannabis. The respected journal Psychiatry Research reports:
“One-hundred and eighty-nine volunteers responded to an anonymous questionnaire inquiring about cannabis use and schizotypal traits (behaviour suggestive of schizophrenia but not of sufficient severity to warrant a diagnosis of schizophrenia). Among recent cannabis users, average age of schizotypal symptoms significantly preceded age of first use of cannabis. When cases were analysed individually, authors affirmed that the majority of respondents in the “recently used” group reported schizotypal personality disorder (SPD) symptoms prior to their initiation of cannabis use.”
The researchers reported an association between cannabis consumption and psychosis, but they went on to clarify:
“The current study suggests a temporal precedence of schizotypal traits before cannabis use in most cases. These findings do not support a causal link between cannabis use and schizotypal traits.”

This paper by Deepak Cyril D’Souza and Richard Andrew Sewell, is well worth a read
“Despite some empirical support for a causal hypothesis between cannabis use and psychotic outcome, most people who use cannabis do not develop schizophrenia, and most people with schizophrenia have never used cannabis”
Download the full report here: Cannabis and psychosis/schizophrenia: human studies
Another paper worth reading on the subject by Deepak Cyril D’Souza states:
“In summary, acute exposure to both natural and synthetic cannabinoids can produce a full range of transient symptoms, cognitive deficits, and psychophysiological abnormalities that bear a striking resemblance to some of the features of schizophrenia. Also clear is that in individuals with an established psychotic disorder, cannabinoids can exacerbate symptoms, trigger relapse, and have negative consequences on the course of the illness”
Download the full report here: A review of the association between cannabis and psychosis

Consuming cannabis at an early age can harm brain cells

There are some indications from a New Zealand study that individuals who smoke cannabis whilst in their teenage years have a lower IQ score in adult life than others who have never used the plant, this suggests that it is not beneficial to use cannabis whilst the brain is still developing.
Yet a North American study conducted by the think tank Source Watch found a correlation between the smoking of certain Sativa strains (high THC) of cannabis and academic achievement. The use of Sativa strains seems to stimulate chords within the cerebellum,  whereas without stimulation they otherwise remain inactive throughout daily activity.
The studies conducted so far have focused on THC, but there has been little if no research on other cannabinoids in teenage use, e.g. CBD. It is evident that more research is needed.

Cannabis causes loss of memory

A clinical trial conducted at Harvard Medical School performed magnetic resonance imaging on the brains of 22 long-term cannabis consumers and 26 control subjects (people with no history of cannabis consumption). The trial reported that imaging displayed “no significant differences” between heavy cannabis consumers and the control group. The authors concluded:
“These findings are consistent with recent literature suggesting that cannabis use is not associated with structural changes within the brain as a whole or the hippocampus in particular”
An animal study in 2008 demonstrated that THC reduced brain inflammation and improved memory in older rats. Subsequent studies indicate that activating the brain’s endocannabinoid system can initiate a type of anti-oxidant cleanse which removes damaged cells resulting in improved brain function.
One of the conclusions by Tabea Schoeler and Sagnik Bhattacharyya:
“the effects are likely to depend on the type of cannabis used (ie, the greater the dose of Δ9-THC, the greater the memory impairment)”
Download the full report here: The effect of cannabis use on memory function

Cannabis can lead to a loss of motivation

Far from having low levels of motivation cannabis consumers are likely to be well educated, well-motivated, and high earners. A survey of 13,900 Canadians conducted by Health Canada found that lifetime consumers of cannabis are likely to be single, well educated, and earn an above average salary. Approximately 45% of the Canadian population (over the age of 15) have reported having used cannabis during their lifetime – up from 23 percent in 1989, the survey reported. Lifetime cannabis use increased with education and income, with 55% of respondents deemed to have a “high income adequacy” reporting cannabis use, opposed to only 43% of those deemed to have a “low income adequacy.”
Sara Smucker Barnwell, Mitch Earleywine and Rand Wilcox:
“The present findings coincide with numerous others studies that cite a lack of evidence for a-motivational syndrome. The majority of chronic cannabis users in the present sample report relatively high levels of motivation comparable to their non-using counterparts”
Download the full report here: Cannabis, motivation, and life satisfaction

Cannabis causes lung cancer

The short answer is, ‘No’. Research suggests that people who smoke cannabis do not appear to be at increased risk for developing lung cancer.
We all know that tobacco smokers run a greater risk of developing lung cancer and other cancers of the head and neck than non-tobacco smokers, however people who smoke cannabis do not experience an increased risk compared with non-cannabis smokers. Studies suggest that marijuana smoke contains up to 50% higher concentrations of chemicals linked to lung cancer than found in cigarette smoke, marijuana smokers also tend to inhale deeper than cigarette smokers and hold the inhaled smoke in their lungs longer.
So why do marijuana smokers not suffer the same incidence of cancer as tobacco smokers?
Unfortunately, the answer is not clear, however cellular studies and even some studies in animal models suggest that THC has anti-tumour properties, either by encouraging the death of genetically damaged cells that can become cancerous or by restricting the development of the blood supply that feeds tumours. University of Colorado molecular biologist Robert Melamede, PhD, has concluded that the THC in cannabis seems to lessen the tumour-promoting properties of marijuana smoke.
An international collaboration into cannabis smoking and lung cancer risk reported:
“No overall association between cannabis smoking and all lung cancer was detected among never tobacco smokers”
Download the full report here: Cannabis smoking and lung cancer risk

Cannabis smoking impairs lung function

Many reports and studies indicate that long-term smoking of cannabis is associated with an elevated risk of respiratory complications, including an increase in cough, sputum production, and wheezing, but not a decline in pulmonary function. Investigators at the Yale University School of Medicine conducted a systematic review of studies published between 1966 and 2005 that assessed the effects of marijuana smoking on pulmonary function and respiratory complications and reported that:
“The data failed to show an association between long-term marijuana smoking and airflow obstruction (emphysema), as measured by airway hyper reactivity, forced expiratory volume (FEV), and other measures, investigators reported”
A New Zealand study of 1,037 individuals who participated in a three-year assessment reported:
“Why smoking cannabis might have different effects on lung function from tobacco is unclear. We found that although both substances were associated with increased lung volumes, there was little evidence of airflow obstruction or reduced gas transfer with cannabis use”
Download the full report here: Effects of cannabis on lung function

Cannabis is certainly no more dangerous than tobacco, and research actually shows that daily cannabis smoking does not lead to increased rates of respiratory illness. Unlike tobacco smokers cannabis smokers suffer no greater incidences of lung cancer than non-smokers.
More information here
If you are concerned about smoking cannabis you should consider vaporising as an alternative. Cannabis vaporisers heat cannabis to a temperature where cannabinoids are released as a vapour (e.g. THC vaporises at 157C) by heating but not burning. The toxins associated with smoking (e.g., carcinogenic hydrocarbons) are not produced.
Clinical trial data published in the Journal of Pharmaceutical Sciences, concluded that:
“vaporisation is a safe and effective cannabinoid delivery system for individuals desiring the rapid onset associated with inhalation, but who wish to avoid the respiratory risks of smoking. The final pulmonary uptake of THC is comparable to the smoking of cannabis, while avoiding the respiratory disadvantages of smoking”
The respected ‘Harm Reduction Journal’ commissioned a report on respiratory symptoms in cannabis consumers who vaporise:
“vaporizer users were less likely to report respiratory problems than participants who did not vaporise, with 100 of 152 vaporiser users (65.8%) reporting no respiratory problems, compared to 3767 of 6731 (56.0%). This analysis provided a rough look at the potential for vaporisers, and suggested that the machines could improve respiratory symptoms”
Download the full study here: Decreased respiratory symptoms in cannabis users who vaporise

Second-hand cannabis smoke can affect non-smokers

Many individuals are incidentally exposed to second-hand cannabis smoke, but little is known about the effects of this exposure. This report examines the physiological, subjective, and behavioural/cognitive effects of second-hand cannabis exposure, and the influence of room ventilation on these effects
“Non-smokers in the ventilated session did not have detectable levels of cannabinoids in blood beyond the initial 30 minutes following the exposure period, did not screen positive on urine tests, and did not report significant increases in subjective drug effects”
“……. findings suggest that ventilation dramatically reduces second-hand smoke exposure, even when large quantities of cannabis (~16.5 grams) are smoked in relatively small spaces in a short amount of time”
Download the full report here: Non-Smoker Exposure to Second-hand Cannabis Smoke

Cannabis today is much stronger and “Skunk” is dangerous

Claims of a dramatic increase in cannabis potency are commonly used by prohibitionists to bolster their dubious case for continuing the failed policy of prohibition. Their argument is based on the assertion that cannabis in the 1960’s and 1970’s contained much lower levels of THC than the cannabis available today. As there are over 5,000 varieties of cannabis in existence the generalisation that THC levels are much higher today is misleading.
Deej Sullivan sums it up in this article:
“The worry is that the government will use this innate distrust of cannabis in the general public to their own ends. If they can successfully convince enough people that ‘cannabis’ is OK but ‘skunk’ is bad, they could derail the legalisation movement”
Read the full article: Here
Before cannabis prohibition drug stores in the U.S. and pharmacies in the UK supplied tinctures of cannabis with up to 40% THC.