All drug use has risks. This page is for information only and does not constitute or replace medical advice. If you have medical concerns about your drug use, please speak to a medical professional.
Cannabis leaf
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Cannabis is the most commonly used illegal drug in the UK. It is a plant that contains hundreds of different compounds called cannabinoids. The main psychoactive cannabinoid is called THC (tetrahydrocannabinol). Other cannabinoids in the cannabis plant include CBD (cannabidiol), CBG (cannabigerol) and CBN (cannabinol). Plants are grown to contain different cannabinoid concentrations and can therefore produce different effects.

Cannabis plants have been a part of human history for thousands of years. The plant material can be used for rope and fibres in addition to being used for medicinal, psychoactive and religious purposes.

Cannabis should not be confused with "synthetic cannabinoids" also known as "Spice".

Other names

weed, ganja, green, grass, pot, bud, hash, resin, shatter, edibles, pollen, squidgy black, soapbar, skunk


Herbal cannabis appears as dried plant leaves or buds in brown/green shades; resin appears as compressed blocks in shades of brown; oils may vary in consistency or thickness and may be amber, gold or dark brown. Oils may be sold in droppers, syringes or capsules.

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Misuse of Drugs Act (1971) – Class B.

Cannabis oils containing any level of THC are illegal to possess, sell, buy or give away.

Penalties for possession are up to five years in prison and/or an unlimited fine. Penalties for supply are up to 14 years in prison and/or an unlimited fine.

How it’s taken

Cannabis may be smoked in a joint, bong or pipe, or vaporised. It may also be found in edible items such as butter, cookies, chocolate, fudge or sweets.

In oil form it may be absorbed under the tongue or swallowed in a capsule. There is also a method of heating oils to a high temperature and inhaling the smoke called “dabbing”.

Oil extracted from cannabis plants can contain varying amounts of THC and CBD. Some may contain very low levels of THC and will not produce a psychoactive effect or very high levels of THC and be much stronger than herbal cannabis.


People using cannabis have reported the following dose/duration of effects, but this cannot be taken as a recommendation: duration and effects of any drug will depend on purity, regularity of use, other medications or drugs you have taken, your body and how it’s taken.

Many people may find that 25mg of cannabis will give them an effect if smoked or vaped. If swallowed or eaten the effects can be felt more strongly from smaller amounts and 5-10mg may produce an effect.

General information on dosing.


Cannabis may make you feel happy, calm and giggly. Some people find that they are more creative and introspective (thoughtful). They may also feel sexually aroused and more connected to the people they are with. 

Other effects can include feeling anxious, paranoid, hungry, sleepy and withdrawn (not feeling like socialising or talking). Often people report a reduction in motivation levels.  

Too much cannabis can cause dizziness and sickness, known as a “whitey” especially when used in conjunction with alcohol. It can also cause dry mouth, red eyes, changes in blood pressure and blood sugar levels and an increase in heart rate.  

The length of the effects is different depending on the way it has been consumed. Generally, if you are smoking or vaping cannabis it will only take a few minutes to feel the full effects. These effects wear off after around an hour and aftereffects may be felt for a few hours  

If you are eating edibles, you will not feel the effects until the cannabis has been processed by the digestive system, so it will take much longer to take effect than when inhaling. The effects can take an hour to come on (but sometimes it is as long as two hours!and can last two to eight hours. 

Cannabis-based medicinal products are legal to prescribe in the UK. When used medicinally, the primary effect is the alleviation of medical symptoms (i.e. prevention of seizures in those with epilepsy) rather than a psychoactive high. 


The effects may vary based on your mood and environment (also known as set and setting). We created a resource on cannabis use during lockdown for 4/20 – find this guide online here.

The effects of cannabis are dependent on the drug (e.g. type, frequency of useroute of administration, dose, legalitypurity), the setting (e.g. environment, company) and the set (e.ghow you feel, expectations of the experience, current health, whether you have eaten).

Download our NEW cannabis resource here.

Harm reduction

If you choose to take cannabis then the following steps can help to reduce harm.


  • Wash your hands for at least 20 seconds with soap and water before handling or preparing drugs. 
  • Wipe down the baggies or other packaging.  
  • Clean all surfaces and equipment regularly including lighters, grinders, vapes or bongs.
  • Avoid sharing drugs from the same baggie or packet.
  • Spend at least two hours researching the drug you are planning to take.
  • Avoid taking drugs alone and have a ‘sober’ friend around if possible. Read our 4/20 resource if you are planning on taking cannabis when you are by yourself.
  • Test the drug. If you don’t have access to a drug checking service, reagent testing kits are available online and can give a greater understanding of what the drug contains, but they may not be suitable for identifying newer compounds or adulterants and can tell you nothing about purity or strength.
  • Occasionally, cannabis products are found to contain synthetic cannabinoids which are difficult to test for without drug checking services. Only buy from someone you know and trust. If the drug smells, tastes or looks different, or gives different effects to what you would expect, avoid taking it/more.
  • Plan your doses and use a watch or timer to keep track of how frequently you are dosing.
  • If you are buying multiple grams at a time, split the drug into smaller bags to help keep track of your use and control how much you are taking.
  • Use scales to measure the dose – you can’t judge an accurate dose just by looking. Start with a small dose and go slow! Remember, that the more of a drug you take, the riskier it is and the more likely you are to experience negative effects.
  • Grind or crush substances down as fine as possible before use. This makes it easier to manage doses.
  • Only carry what you plan on taking. If you have a couple of grams in your pocket it is easy to take more than you anticipated. Leave what you don’t need at home (in a safe place).
  • Stay with people you trust, in a safe environment and be aware of dangers, such as water (e.g. rivers, lakes) and sharp or hot objects.
  • Drugs can lower inhibitions and increase the likelihood of taking risks related to money, sex and other behaviours. Before you take drugs, set yourself some boundaries and try to stick to them.
  • Avoid mixing different drugs including alcohol and medicines as this can cause unintended or unpredictable effects. Take time to research possible interactions with your medication or health condition.
  • If you do mix drugs, do your research, ensure you are somewhere safe and take way less of both substances than you would if you were only taking one.
  • Mixing cannabis with other drugs that produce a psychedelic effect can lead to a more intense experience – be aware of this if thinking of mixing with drugs like LSD, magic mushrooms, ketamine or 2CB
  • If you do feel any negative effects remember that these will pass – telling a friend and changing your environment may help ease these feelings.
  • Cannabis can affect your short-term memory (while using cannabis.)
  • Increasing tolerance (needing more cannabis to feel the same effect as before) can be a sign of dependency. Think about taking a  “T-break” every once in a while (‘T’ standing for tolerance). Worried about your use of cannabis? Use our Check-it out tool here.
  • Remember that you will feel the effects more strongly from a smaller amount of cannabis after a tolerance break.
  • People with existing mental health issues may want to avoid cannabis as some people can be more vulnerable to the potential negative effects of cannabis.
  • There is a risk to an unborn child if used during pregnancy.
  • It also remains a Class B drug, although in Scotland the police may instead issue a Recorded Police Warning to deal with ‘low level offences’ such as the possession of a small amount of herbal cannabis.
  • In Scotland, it is a crime to drive with a specified controlled drug in the body, in excess of a specified limit. This includes cannabis. Police can make a requirement for a roadside drug test if they suspect drug use (e.g. smell cannabis), you commit a moving traffic offence (e.g. speeding or driving with a faulty light) or after any accident, regardless of fault. The length of time a substance can be detected varies and can depend on the dose, type and personal factors. Only drive if you are sober, feel well and aren’t sleep deprived.


Cannabis can be smoked in a joint (as pure cannabis or mixed with tobacco) or packed into a pipe or bong. Inhaling smoke can damage the mouth, throat and lungs and can cause breathing difficulties, wheezing, chest pain, shortness of breath and in extreme cases, respiratory disease and respiratory failure. 

  • Use glass or metal pipes as these give off less fumes than wood and plastic. 
  • Clean pipes and bongs regularly. If using a water bongchange the water after every session. 
  • Use a grinder to grind herbal cannabis down finely before use. This makes it easier to judge a dose and helps it to burn more effectively. 
  • Hash can be broken from the main block into small pieces or rolled into a long snake. It may need to be heated with a flame to crumble small parts off. Take care to roll hash into small, thin pieces. If the pieces are too big, they can fall from a joint when smoked (hot rocks) and cause burns. 
  • Sharing pipes, bongs, joints/spliffs can spread infections and viruses – only use your own.
  • Use a charcoal filter as they filter out more toxins than roaches (filters made using rolled cardboard).
  • If you are using a roach, use a long piece of unprinted card to avoid inhaling ink chemicals. Unbleached and sustainable rolling papers and filter card are available. 
  • Smoking cannabis with tobacco puts you at risk of nicotine addiction, and all the harms of tobacco smoke. Reduce the amount of tobacco you take, or better still – leave it out completely – this might be easier if using a pipe/bong or vape. For help to stop smoking, visit NHS Inform.
  • Take one or two draws and then take a break to let the effects come on before taking more. The risk of the effects being overwhelming is increased if you take too much too quickly – dose low, go slow! 
  • Avoid holding smoke in your lungs – this will not increase the high but can cause more damage to your lungs. 
  • Ensure all joints are fully extinguished before leaving the room or going to sleep. Avoid smoking in bed.


vapouriser heats the cannabis, rather than burning it. This still releases the flavour and cannabinoids, but without the smoke. As fewer chemicals are released, vaping is a less harmful way to consume cannabis than smoking, however it is not risk free.  

  • Sharing vapes and e-cigarettes can spread infections and viruses – only use your own equipment. 
  • Take one or two draws and then take a break to let the effects come on before taking more. The risk of the effects being overwhelming is increased if you take too much too quickly – dose low, go slow! 
  • Clean the vape regularly. 
  • Buy a good quality vapouriserThere is a risk of burns and fire from poor quality equipment. 

If vaping herbal cannabis: 

  • Grind herbal cannabis before packing it into the vapouriser. 
  • Herbal cannabis is best vaped using a dry herb vape, rather than a regular e-cigarette vape (although e-cigarette adaptors may be available)Putting oil into a dry herb vape will damage the device.
  • Dry herb vapes work by heating a small chamber in the device. Take care to let the device cool down between uses to avoid overheating.  

If vaping cannabis oil: 

  • Buy good quality oil. Be aware that poor quality oil may contain contaminants which can be harmful to your health.


 Dabbing is a method of inhaling cannabis concentrates by dropping a small amount on a hot surface and allowing it to vapourize. 

  • Clean the rig (bong-like glass device) regularly. 
  • Sharing rigs can spread infections and viruses – only use your own equipment.
  • Break the concentrate into tiny pieces.
  • Cannabis concentrates contain high levels of THC. Take one draw and wait for the effects to come on before taking more. The risk of the effects being overwhelming is increased if you take too much too quickly – dose low, go slow! 
  • Avoid holding smoke in your lungs – this will not increase the high but can cause more damage to your lungs. 
  • The equipment can get very hot, take regular breaks to allow it to cool down.Page Break 


When cannabis is mixed into food or drink it is known as an edible. Cannabis is not water-soluble, so the cannabinoids are extracted by cooking it in a fatty substance like oil, cream or butter which is then used to make food such as cakes, chocolate and sweets.   

  • Spend time researching the effects and average dose. Be aware that the average edible dose is far smaller than if inhaling 
  • It can be more difficult to judge a dose if it has been put into food, and therefore it is easier to take too much. Dose low – remember you can always take more but you cannot take less. 
  • If buying a commercial cannabis edible, the manufacturer should list the THC levels on the packet. Take care to notice if this dose is for the whole product or just one portion. Many commercial edible products contain multiple doses per packet. 
  • It takes longer for the effects of cannabis to come on when it is eaten. Start by eating a small piece or one dose and wait at least two hours before taking more. 
  • Getting the ‘munchies’ is a common effect from cannabis. Buy normal snacking food, so that when you feel hungry you do not eat more of the edible and redose. 
  • Keep edibles away from others, especially children and pets. This is true for all drugs but pay particular attention with edibles as they can easily be mistaken for treats. 

Detection time

People taking cannabis have reported the following detection time, but this cannot be taken as a recommendation; detection of any drug will depend on purity, regularity of use, other medications or drugs you have taken, your body and how it’s taken.
  • 3-30 days in urine depending on frequency of use or up to 12 weeks with long-term use