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Cannabis is known for its pain-relieving and mind-altering properties. There are many different strains (species) of the cannabis plant, and all of them have different chemical compositions and effects. Scientists are still identifying new varieties, each with a different chemical make-up, while also making new discoveries about cannabis’ therapeutic potential. Nowadays, cannabis is the most-used illicit drug in the world. While it is safer than other drugs, such as alcohol, cannabis has negative effects on health.
It's not harmless
Cannabis is not harmless: there is harm and addiction can occur.
When feeling unwell after using cannabis, the road to recovery involves drinking plenty of water, consuming some sugar, lying down and avoiding drugs for the rest of the day.
Careful with edible cannabis products. It is the easiest way to overdose. Don´t take more than has been recommended, even if the effects take longer than expected.
We have listed the most common effects of cannabis. Please note that everyone can be affected differently, and this is not an exhaustive list. Not everyone experiences these effects, and other effects are possible.
The likelihood of feeling these effects, and the strength of the sensation, depends on the THC:CBD ratio of the cannabis.
The effects are (from positive to negative):
- Feel relaxed
- Talkative and sociable
- Slurred speech
- Distorted sense of time and space
- Alteration of sight and smell
- Loss of pain perception
- Impairment of short-term memory
Dose and onset
How? How Much? When? For how Long?
The effects you experience from a given dose of cannabis depends on many different details about the user, such as their weight, the speed of their metabolism, their past experiences and the situation in which the cannabis is consumed.
The same is true of every other drug, but with cannabis, it is especially difficult to identify one’s ideal quantity, due to the variety of strains, the way you consume it, and the distribution of the active compounds in the buds.
How you take it matters...
From the healthiest to the most harmful way:
This route of administration is the healthiest, but it can only be obtained with a medical prescription in countries where this is legal and sold. As such, it is barely used among recreational drug users, who for the most part are left with more calorific or carcinogenic alternatives. Sativex is the most widely-known spray. It contains high levels of both THC and CBD, and takes around 15 minutes to kick in.
Vaping involves heating up cannabis to release THC and other cannabinoids. Vaping is, crucially, a cleaner alternative to combustion (i.e. smoking/inhaling). The heating process creates a temperature cool enough to avoid creating the toxins that appear during combustion. Therefore, vaping is likely to reduce the coughing and throat irritation associated with smoking. It also doesn’t require any tobacco, and therefore may reduce tobacco addiction in cannabis users (3,7,8). This may be the most expensive method of administration, because of the price of the vaporiser. However, vaporising could be a cost-effective method in the long term8,9.
Read about how vaporisation works.
Eating is probably the easiest and safest way to consume cannabis. However, eating cannabis is not without dangers: users anticipate similar timing and effects to when they are vaping/smoking/inhaling, but the effects take much longer (up to 2 hours) when consuming edibles. Therefore, it’s tempting to re-dose before the high comes on. Be patient: if the first dose wasn't strong enough, try a higher dose another day. Re-dosing is the easiest way to overdose! People normally feel that edibles give them a “body high,” this is because the compounds in cannabis are slightly altered by the stomach, intestine and liver.
Cannabis can be inhaled through a pipe or a bong. While it's less harmful than smoking, it is easier to inhale greater quantities of smoke. Users should be careful not to breathe too deeply in order to regulate their high. Bongs with ice catchers can reduce the irritation of the throat as the ice cools down the smoke.
Smoking cannabis is the most common way to consuming cannabis, even though it’s the unhealthiest. This method increases the probability of developing lung cancer because burning cannabis (with or without tobacco) creates toxins associated with cancer. In Europe, cannabis is often mixed with a much deadlier companion: tobacco. Adding tobacco to your cannabis increases the chances of throat irritation, and also increases the risks of cancer and dependence. We recommend to avoid smoking cannabis, but if you do instead of using tobacco you could use herbal smoking blends without nicotine and other toxins found in tobacco.
Every time you try a new strain, or use a different supplier, smoke a smaller dose than you are used to, so you can notice variations in the effects and potency of the drug (we define potency as the amount of active ingredient required to produce a desired effect).
- Light dose: 0.05 g
- Common dose: 0.15 g
- Strong dose: 0.25 g
For someone consuming the average dose, a one gram bag of cannabis will last between 8–12 smokes, if you roll your joints with king skins and mix your weed with tobacco.
When you cook edibles, there are even more factors that influence the effects you'll get from the food. Some of these are: the strain you are using, whether you are using oil or butter, the time you leave it cooking, the strength of the heat (low heat, between 1-2 hours in a saucepan is optimum), and of course, your culinary skills...
- Light dose: 2-4 mg
- Medium dose: 3-8 mg
- Strong dose: 4-15 mg
When do the effects kick in?
The START time below is when you will usually begin to feel the effects of cannabis from the time when you first take it. DURATION is roughly the length of time you will experience the effects, after which the effects will start to wind down and you might start to feel the comedown effects.
- START: 2-10 minutes
- DURATION: 2-8 hours
- START: 20-120 minutes (depends on stomach content)
- DURATION: 3-9 hours
Kief is the resin that falls off dry cannabis or what accumulates in grinders. It is the strongest part and contains high concentrations of THC. Watch out for this.
How often can I take it?
Consuming cannabis too often decreases the potency of this drug on your body. This may lead to consuming larger amounts of cannabis. Save cannabis for special occasions or events only, and use it sparingly.
Tobacco and cannabis are often used together and have a unique relationship. In a recent worldwide survey, 65% of respondents said they smoke joints made with cannabis and tobacco. Studies indicate that the likelihood of developing cannabis dependence is increased by 5 times when cannabis is smoked with tobacco, as opposed to on its own e.g. smoking cigarettes and cannabis, and together, in joints. Often, users pair the two because the tobacco acts as an inexpensive filler.
A hypothesis suggests that this increase in addictiveness may be a two-way street, with the cannabis enhancing your likelihood of developing nicotine dependence. Being addicted to nicotine is thought to go hand-in-hand with poorer psychiatric and psychosocial conditions.
Finally, the World Health Organisation notes that smoking-related deaths are the most preventable kind in the world. So it’s imperative that alternative methods of consuming cannabis are used. However, smoking cannabis with tobacco is still the go-to method in most countries around the world.
Written by Chandni Hindocha, PhD student at UCL
There are certain precautions you should take before using cannabis. The advice below helps to prepare you both physically and mentally. We want you to be safe and enjoy your experience as much as possible, so if you have a bad experience or are struggling with especially bad after-effects, please take note of the advice below.
It is common to mix cannabis with tobacco to consume the former. However, this habit increases the chances of dependence and of developing cancer. We recommend to avoid smoking cannabis, but if you do instead of using tobacco you could use herbal smoking blends without nicotine and other toxins found in tobacco.
GET SOME WATER
While you are under the effects of cannabis, you should drink regular water to avoid feeling unwell. People tend to forget about drinking water, so try to get some water in advance.
Try not consume cannabis alone, this will increase the chance of unpleasant experiences, unsafe circumstances, and dependence. You should also avoid smoking to numb anger or sadness, this can lead to bad experiences too.
Cannabis can have some hallucinogenic effects and it can sometimes make people paranoid. To avoid bad experiences, try to consume cannabis in a comfortable and safe space.
In recent years, the potency of cannabis in the UK has been increasing, i.e. the concentration of the major psychoactive cannabinoid in cannabis, THC, has increased. Within the same time-frame, the number of young people seeking treatment for cannabis dependence has also increased5,10. This upsurge is thought to be due to the rising THC levels. At the same time as THC levels have risen, there has been a corresponding decrease in the amount of the primary non-psychoactive, and possibly protective, cannabinoid called Cannabidiol (CBD)14.
Cannabis users are advised to smoke varieties of cannabis that are high in CBD e.g. resin/hash and to avoid 'skunk'. If you don't have much experience with cannabis, you are more likely to get paranoia if the strain is low in CBD and high in THC.
Written by Chandni Hindocha, PhD student at UCL
It's very uncommon, but you might feel unwell after consuming cannabis. It can happen to anyone, although it is more common in first-time users. Surprisingly, it can occur with low or high doses and with a strain you have tried before. When this happens, people generally feel nausea, paranoia and look pale.
To help yourself or a friend consider doing the following:
- Drink some water and consume sugar. Be careful with overeating or drinking too much: take water in short sips and eat small bites, take your time to chew and swallow.
- Lie down and take deep breathes. Slow down your breath rate.
- To help someone who is whiteying: talk slowly and calmly to the person. Find out if he/she needs conversation and attention or prefers silence and some time on their own. Provide them with water and something to eat. Help them breathe deeply and at a constant pace.
- Take it easy for the rest of the day and rest. You should not consume more drugs even if you feel full of energy again, as your body will be less well-equipped to process them.
Some people observe feeling “hungover” after consuming weed, others don't.
You may experience some of the following:
- Dry itchy eyes
- Grogginess or spaciness
- Feeling of being in slow motion
- Mild nausea
The best advice we can give to reduce hangovers is to drink plenty of water and get enough sleep!
Contrary to what many weed smokers believe, addiction and dependence can occur when using cannabis. Medical practitioners call it Cannabis use disorder. However, it seems to be true that cannabis shows much lower dependency rates than other recreational drugs, such as alcohol and nicotine.
Read more about dependence here.
In the long term
Cannabis can have long-term effects when used heavily (i.e. daily or almost daily).
However, all the negative effects of cannabis seem to wear off after a relatively short period of total abstinence, usually 4-6 weeks1, 2.
Cannabis compounds affect a system that is crucial for the development of your brain. Therefore, people who started using cannabis during adolescence may develop:
- Impaired spatial orientation
- Impaired verbal fluency
- Reduced inhibition
In terms of the effects on daily users, there are discrepancies in the scientific literature on the subject. But the most common negative effects are thought to be4, 16:
- Difficulty making decisions
- Difficulty learning new things
- Difficulty making future plans
If you mix cannabis with tobacco, you significantly increase the harms, and aggregate the risks of developing health problems.
Check and compare your drug use anonymously with the Drugsmeter Cannabis app.
Learn more above in the "How you take it matters" section.
Interestingly, THC has been found to stop tumours' growth and metastases. In several studies, cannabis smokers (using only pure cannabis) were found to have a reduced risk of lung cancer. Although THC has a beneficial effect on cancer cells, you need to look for balanced levels of THC:CBD, in order to reduce the harm to your brain.
Chronic obstructive pulmonary disease is a broad term that includes different lung diseases. They all result in difficulty of breathing.
Watch this video if you want to know more about medical cannabis and its impact on human health.
When you want to quit...
While withdrawal symptoms are mild and can be easily overcome, weaning yourself off weed does have some unpleasant effects. As with every single drug, the intensity of the withdrawal depends on the quantity you’ve trained your brain and body to tolerate/expect.
Here are some psychological and physical withdrawal symptoms you may experience when you are trying to quit:
- Insomnia and nightmares
- Lack of enjoyment
- Aggressiveness and/or anger
- Unpleasant corporal symptoms
- Decreased appetite
- Weight loss
- Mood changes
Remember: Don't hesitate to look for medical help: you won't get in trouble.
Nicotine is often consumed with cannabis. Some withdrawal symptoms are common for most recreational drugs, but for daily users of cannabis and tobacco combined, the double withdrawal is stronger than if you choose to consume cannabis on its own. This is another great reason to go for vaping/eating.
- UK: Illegal Class B drug. Possession: up to 5 years in prison, an unlimited fine or both. Supply and production: up to 14 years in prison, an unlimited fine or both.
- France: Illegal but permitted for medical products.
- Germany: Not prosecuted up to 6-15 grams depending on the Ländern. Only legal when a permission by 'Federal Institute for Drugs and Medical Services' for medical use is obtained.
- Netherlands: Legal (less than 5 grams is considered personal use).
- Norway: Legal (less than 15 grams is considered personal use).
- Spain and Portugal: Legal (only private growing and smoking are legal).
- Switzerland: Legal (growing up to four plants is legal).
- Russia: Illegal, but decriminalised up to 6 grams.
- USA: Illegal at the federal level, but legal for medical/recreational use in the states of Colorado, Washington, Alaska and Oregon as well as in some cities.
- Canada: Legal everywhere in Canada since October 17th 2018.
- Mexico: Possession is illegal but decriminalized up to 5 grams. Growing and selling are illegal.
Asia and Australasia
- Australia: Illegal, but decriminalised in some states.
- New Zealand: Illegal.
- Singapore: Illegal.
- Hong Kong: Illegal.
- Israel: Illegal.
- South Africa: Illegal.
Watch this video on why cannabis was criminalised: