Cannabis and Your Health - HE1404

June 2019
This resource relates to the following topics:

Information about the possible effects of cannabis on health, including when cannabis is used with other drugs such as alcohol and tobacco.

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June 2019
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Photo of a cannabis plant – this is a bushy plant, with slender, pointed leaves.This pamphlet provides factual information about the possible effects of cannabis on your health.

Any drug can cause harm and cannabis is no exception. The same goes for legal drugs like alcohol and tobacco.

While cannabis is illegal, some people still choose to use it. If you choose to use cannabis, you should know the full facts about how it might affect you.

There are also some situations where the chance of harm from using cannabis may be greater – such as when you are:

  • feeling depressed or stressed
  • trying to focus on study or school work
  • driving a motor vehicle or operating dangerous machinery, especially when mixing cannabis and alcohol.

Photo of a sack of harvested cannabis. There are also times when using cannabis can put you at a disadvantage in relation to others, such as using it before you play sport, doing things requiring co-ordination, or when it’s important that you concentrate.

This information will help you make a more informed decision about using cannabis and may help reduce any harm cannabis could cause you.

What is cannabis?

Cannabis is a drug prepared from the plant cannabis sativa. The three common forms of cannabis are:

Marijuana – the small stalks, dried leaves and flowering tops (‘buds’). It is usually smoked in a hand rolled cigarette or ‘joint’, or inhaled through a pipe or bong; it may also be eaten in cakes or biscuits.

Hashish – dried resin and compressed flowers that usually comes as a block.

Hash oil – sticky concentrated liquid made from leaves and buds.

How does cannabis work?

Photo of a pile of cannabis buds.The chemical in cannabis that causes you to get ‘high’ or ‘stoned’ is called THC (delta-9-tetrahydrocannabinol). When cannabis is smoked or eaten, THC enters the bloodstream and goes to the brain. When in the brain, THC binds to tiny parts of the brain called brain receptors. If enough THC binds with these brain receptors, your behaviour will be affected and you become ‘stoned’.

What are the possible effects of using cannabis?

The effects of using cannabis can be put into two separate groups:

  • immediate/short-term effects
  • long-term effects.

Immediate/short-term effects

These are the likely short-term effects of a single dose (eg, after smoking one or more joints in a session). These effects can happen soon after the drug is in your system or while you are ‘stoned’ and can last up to 3–4 hours. They may include:

  • Photo of a capsule of hash oil, which is about 2 centimetres long.increased heart rate and changes in blood pressure
  • feelings of happiness and relaxation
  • talkativeness and laughter
  • changes in mood, perceptions, thoughts or feelings
  • possible paranoia, anxiety, or panic
  • feeling of hunger – ‘the munchies’
  • time seeming to speed up or slow down
  • some experiences seeming to be intensified
  • impaired reaction time and co-ordination that may lead to a higher risk of accidents
  • impaired concentration, short-term memory, and information processing that affects learning at school or work performance
  • potential worsening symptoms of mental problems in those with a history of such problems.

Whether you experience these effects as positive or negative or a mix of both will depend on various factors. These include your previous experience with cannabis, the amount you use, your mood at the time, or the environment in which you use the drug.

Long-term effects

Photo of a bag of cannabis and a deal bag. These are the possible long-term effects of regular cannabis use (eg, after smoking daily or regularly for a period of years). These effects may include:

  • breathing system problems – eg, bronchitis, emphysema, wheeziness, shortness of breath
  • becoming dependent on cannabis, so that you are unable to stop using cannabis or control your use. Risk of dependency appears greater if you start using cannabis at an early age
  • subtle impairments to your thinking processes – such as organising complex information and using your attention and memory processes. It’s unclear if such effects are reversible. 
  • increased risk of cancers of the lung, mouth, throat, and the canal from mouth to stomach
  • possible impaired educational achievement in adolescents, and underachievement in adults’ work performance if their work requires high-level thinking skills
  • a risk of worsening symptoms for those with physical problems (such as breathing-system problems) or mental problems (such as schizophrenia)
  • if you smoke while pregnant, your baby could be affected (eg, born with a low birth-weight)
  • a possible increased risk for some young people using cannabis to be exposed to other drugs.

Additionally, if you use cannabis regularly, it may lead to problems relating to family and friends.

The evidence for some of these effects is complex and cannot all be summarised in a pamphlet. For more detail, check out the websites listed at the end of the pamphlet.

Will cannabis always produce the same effects?

No. The effects of cannabis can be different each time someone uses it and can also be different for different people. The effects of cannabis depend on:

the drug – How much cannabis is used and its strength will affect its impact. Generally marijuana is weaker than hash and hash is weaker than hash oil. Using other drugs with cannabis, such as alcohol, creates different effects, and does not cancel out the effect of either cannabis or alcohol or any other drug.
the person –  The user’s mental state (eg, mood) and physical characteristics, along with past experience with cannabis will also affect reactions to the drug.
the setting – The environment in which cannabis is used can also play a part. If you are with people you know and in a familiar place, you may experience fewer feelings of anxiety or paranoia than you would if you were in a strange environment or something unexpected happened.

Photo of small ziplock bags containing cannabis, for dealing.The occasional use of cannabis may not cause the average person significant harm. However, the risks of short-term harm will increase if cannabis is used in situations when it’s important to concentrate or be totally physically co-ordinated (eg, driving). Risks also increase if your mental state and physical characteristics mean that you react negatively to the drug.

The risks of long-term harm will increase if you use cannabis regularly or heavily over a long period of time (eg, daily or regularly over a number of years).

Where do I go for more information about cannabis and other drugs?

Photo of tinnies for dealing in small quantities.The scientific evidence about the health effects of cannabis is complex and there are some gaps in our knowledge.

For more information and help for those worried about their own or someone else's cannabis use, go to

Information about cannabis is available for young people on the Urge/Whakamanawa youth website – 

Where do I go for help?

If you or someone you know needs help for a problem with cannabis, contact one of the following services:

Alcohol Drug Helpline

0800 787 797 (10am–10pm seven days a week)

Narcotics Anonymous Wellington: 04 801 9933
Auckland: 09 303 1449
Christchurch: 03 365 0686
Alcohol and Drug Treatment Services phone your nearest hospital
Youthline 0800 376 633
Citizens Advice Bureau 0800 367 222
Your doctor or a local GP look under Registered Medical Practitioners at the front of your phone book
Emergency dial 111 for an ambulance