New Zealanders are going to the polls on September 19 to vote whether to legalise the recreational use of cannabis or not.
We have been taught to consider cannabis as a dangerous substance for 50 years through publicity aligned with the so-called "War on Drugs", a global movement initiated by US President Nixon's declaration in 1971 that drug abuse was "public enemy number one".
At the same time, we have been taught that alcohol is not only relatively harmless but that it is entirely normal to consume alcohol most days of the year and that drinking alcohol regularly makes us successful citizens.
This marketing of alcohol has been buttressed by backroom lobbying of successive governments to prevent stronger regulation of alcohol. The result of all of this propaganda and pressure is a strong tendency for us to think of alcohol as good and cannabis as bad.
But we can look at how alcohol and cannabis line up according to 13 commonly discussed issues related to drugs and health.
This can be done by comparing delta-9-tetrahydrocannabinol (THC), the primary psychoactive drug in cannabis, and ethanol (ethyl alcohol), the generic name for the alcohol in our beverages.
The descriptors of harm are, in some cases, based on very solid information, such as the overdose and cancer risks, whereas other aspects, such as whether cannabis causes brain damage and depression, are not so clearly established by existing research.
Alcohol is more harmful than cannabis on nine of these 13 aspects and, for at least seven, alcohol is significantly more harmful.
In the instance of risk of death from overdose and severe withdrawal, it is almost impossible to die from a cannabis overdose, whereas one New Zealander dies of an alcohol overdose every week or two, and severe alcohol withdrawal is the most lethal of the substance withdrawal syndromes.
For risk of aggression during intoxication, every weekend and many weekdays, New Zealand's "vibrant" social life is marred by physical and sexual assaults. Our appalling alcohol-fueled family violence statistics continue year after year.
For risk of brain damage including fetal brain damage [alcohol is more harmful than cannabis] due to the direct neurotoxicity of alcohol; with risk of liver and other organ damage, alcohol is associated with more than 200 medical conditions.
As to whether they are known to cause cancer, breast cancer is the number one cause of an alcohol-related death in New Zealand women, a fact the alcohol industry works hard to keep from its customers. Alcohol also contributes to the risk of bowel cancer, another of our commonest cancers, and at least five others.
There is only one health aspect, "anxiety during intoxication", where cannabis is distinctly more harmful than alcohol. Alcohol dissolves anxiety in most people, whereas cannabis can heighten feelings, including anxiety in some people. There will be a presentation to emergency departments most months of an inexperienced user of cannabis with a panic attack.
The one harm often pointed to as evidence of the danger of cannabis compared with alcohol is "known to cause psychotic conditions". In fact, both cannabis and alcohol are known to cause psychotic conditions, but in both instances, these are rare events, and generally occurs following chronic heavy use of potent forms of either drug, especially when there is a family history of psychosis.
Nevertheless, cannabis has been singled out as a psychotogen because it is known to change people's perceptions. Some researchers have labelled these perceptual changes "psychotic" although the vast majority are "psychotic-like".
In addition to seeking a change in mood, users of cannabis generally enjoy changes in their perceptions and accompanying thoughts as well; such as experiencing time going slower, having surprising new ideas or a deeper sense of meaning about normal routines or ordinary objects, or having a greater appreciation of music. A small minority of users view cannabis as a spiritual aid.
The differential harm profile demonstrates how irrational our drug laws are. If the choice was to have just one legal drug it would make more sense for cannabis to be legal and alcohol to be illegal, based on health harms. But we are voting whether to add cannabis to the choice of legally available recreational substances or not.
A "no" vote in the upcoming referendum should not be based primarily on the potential health harm from cannabis unless we are also advocating for alcohol use to be made illegal.
On the other hand, to vote "yes" requires us to trust the door isn't being opened to big business to ultimately control and exploit cannabis.
Big business involvement in alcohol has clearly increased alcohol harm and this would almost inevitably be the case for cannabis as well.
However, societal harm is likely to be at a lesser extent overall compared with alcohol because cannabis is inherently safer than alcohol.
• Doug Sellman is Professor of Psychiatry & Addiction Medicine at the University of Otago and medical spokesman for Alcohol Action NZ.