Is cannabis more potent than it used to be?

On the available evidence it would appear that the strength of cannabis has increased to some extent over the last 25 years. The reported changes in strength may be partially explained by different patterns of use and the increased availability of the stronger part of the plant. It should be noted that:

• potency data is not routinely collected in Australia so it cannot be determined whether the cannabis used here in Australia has become more potent over time
• reported changes in strength could be due to changes in patterns of use, i.e., people are more likely to smoke the stronger part of the plant – the ‘heads’
• in the USA, THC levels of cannabis have risen over the last 25 years, from about 4% in 1983 to 9% in 2007
• in New Zealand, the potency of THC has not changed
• in Europe, cannabis potency has remained the same in some countries and increased in others

Can cannabis cause violence?

Cannabis is less likely to cause violence than other drugs such as alcohol or amphetamines. Cannabis users who commit violent acts typically have a history of violence before they first use the drug. Cannabis withdrawal may cause aggressive behaviour because of the irritability associated with it.

Does cannabis cause people to become ‘demotivated’?

A lack of motivation is often reported by cannabis users. This is more likely to be due to the regular user being depressed and/or chronically intoxicated rather than a particular effect of use.

• the ‘amotivational syndrome’ can be characterized by a loss of interest, being less productive, having difficulty in carrying out long-range plans, tiredness, depression, and difficulties with concentration and attention
• it is commonly reported among those in cannabis treatment but not among cannabis users generally

What are the effects of passive cannabis smoking?

Cannabis smoke contains many of the dangerous substances that are found in tobacco smoke, such as tar, carbon monoxide and cancer-causing chemicals, and can therefore cause similar problems to those experienced by passive tobacco smokers.

Traces of cannabis can be found in body fluids as a result of passive cannabis smoking.

• a recent study compared tobacco and cannabis smoke and found that directly inhaled cannabis smoke contained 20 times as much ammonia and 5 times as much hydrogen cyanide as tobacco smoke. Nitrogen oxides were five times as concentrated in cannabis smoke
• it also measured the chemicals found in ‘sidestream smoke’, which would account for 85% of the smoke inhaled during passive exposure. It found that it contained higher concentrations of almost every chemical measured than inhaled smoke

Is cannabis a gateway drug?

Most people who use illicit drugs first used drugs like alcohol, tobacco or cannabis. However, the vast majority of people who use cigarettes, alcohol or cannabis never use other illegal drugs, e.g. only 4% of cannabis users have ever used heroin.

Cannabis use, however, particularly regular use at a younger age, increases the risk of other drug use.

• most users of heroin or amphetamines first used cannabis
• there is a greater risk of other illicit drug use and dependence among those who begin cannabis use in early adolescence

The link between cannabis use and the use of other illicit drugs is usually due to personal traits that make it more likely for the person to take part in risky behaviour, e.g. associating with drug using peers.

What do we know about mixing alcohol and cannabis together?

If more than one drug is used at one time, the more unpredictable are the effects. This is the case when alcohol and cannabis are used together. Having alcohol in a person’s blood can cause more THC to be absorbed into the blood, leading to an unpleasant effect. It also compounds the negative effect on driving performance and other motor skills.