What are the effects of cannabis use?

Cannabis is the most used drug in Ireland and is known to cause a range of side effects.  

In this article, we take a closer look at cannabis, what it does to the body, the short-term and long-term effects of cannabis use, and how long cannabis stays in your system.

What is cannabis?

Commonly referred to as marijuana, weed, dope or hash, cannabis is a plant-based drug derived from the Cannabis sativa or Cannabis indica plant.

Popular among recreational drug users, it is often sold as a soft lump of dried green or brown herbs. However, it comes in many different forms including skunk, which is a particularly strong strain of the substance that is bright green and covered in crystals.

Cannabis is most commonly smoked or vaped, but some people also add it to food and drink products known as ‘edibles’ or ‘cannabis edibles’.

Other forms of cannabis include cannabidiol (CBD), a cannabinoid commonly sold online and in select shops in the form of CBD oil, and cannabinol (CBN), a compound found in the cannabis plant that produces few, if any, psychoactive effects.

In Ireland, cannabis is controlled under the Misuse of Drugs Act 1977 and 1984. This means that it is an offence to have cannabis in your possession either for personal use, or with the intent to supply.

The penalty for cannabis possession can include a fine, prison sentence, or both. However, several factors will be considered for sentencing including the type, quantity, and total value of the drugs found.

What does it do to your body when you take cannabis?

It is important to remember that drugs affect people in different ways. Not everyone will have the same experience with the same substances, and drugs can even affect the same person differently when taken at a different time.

Cannabis is a psychoactive drug. The effect it has on the person taking it can depend on a variety of factors including the kind of person they are usually, their mood when taking it, how much cannabis they have taken, frequency of use, and how much tetrahydrocannabinol (THC) the drug contains.

THC is the main psychoactive compound found in cannabis. When a person uses cannabis, THC is released into the system. This alters normal brain communication and affects emotions, thinking, memory, concentration, and movement.

Some people might feel relaxed and giggly after using cannabis while others can become anxious and paranoid.

Other side effects of cannabis include increased hunger and drowsiness. In some instances, sickness and nausea can occur, as can mild hallucinations.

Long-term use has also been linked to mental health problems such as depression and anxiety.

Is cannabis addictive?

Yes, cannabis is addictive. People who use cannabis regularly may experience cravings and withdrawal symptoms when they stop using it, leading to the development of harmful addictions.

When an individual ingests cannabis, either through smoking, vaping, or eating it, this alters the way the brain works and causes it to release dopamine.

Dopamine, the brain’s ‘feel-good’ chemical creates feelings of euphoria, pleasure, and reward. These powerful sensations cause some people to become addicted and dependent on cannabis.

People who use cannabis on a regular basis are also more likely to build up a tolerance to it. This means that they will require even more of the drug over time to experience the same ‘high’.

What are the physical effects of cannabis use?

Although the effects of cannabis can wear off in as little as an hour, depending on how much of the substance was consumed, using cannabis regularly has been linked to several physical health problems including:

  • Breathing issues
  • Increased heart rate and blood pressure
  • Coughing
  • Fertility concerns
  • Insomnia/difficulty sleeping

Short-term physical effects of cannabis can include increased hunger, nausea, vomiting and drowsiness.

How can cannabis impact your mental health?

As well as the potential for developing physical health problems, people who use cannabis on a regular basis also put themselves at increased risk of developing psychological and mental health problems.

Heavy cannabis use has been linked to:

  • Hallucinations
  • Paranoia
  • Memory problems
  • Psychotic disorders, including schizophrenia
  • Depression
  • Anxiety

What are the long-term effects of cannabis use?

The effects of cannabis can wear off in as little as an hour, depending on how much cannabis was consumed.

However, cannabis use over a prolonged period has been shown to cause several long-term effects and increase the risk of serious health problems, including:

  • Heart and blood pressure issues
  • Breathing difficulties
  • Fertility concerns
  • Mood swings
  • Difficulty sleeping
  • Poor mental health episodes

Can cannabis be used for medical purposes?

Although rare, cannabis-based medicines may be prescribed in Ireland on a case-by-case basis to relieve symptoms of certain conditions, where standard therapies have failed or have been deemed unsuitable.

People with the following conditions may be eligible for access to medicinal cannabis:

  • Multiple sclerosis
  • Nausea and vomiting associated with cancer treatment (chemotherapy)
  • Severe, treatment-resistant epilepsy, where anticonvulsant medications have not worked

How long does cannabis/THC stay in your body?

When a person consumes cannabis a proportion of the drug and its metabolites are released into the body and bloodstream.

A small amount of the drug is then excreted from the body in a variety of ways.

How long cannabis and THC remains in the system and how quickly someone might feel the effects depends on how the drug was consumed, frequency of usage, how much cannabis was taken, how much THC is in it and the weight and metabolism of the individual.

When smoked, cannabis and its effects can be felt in as little as one minute. When eaten, the effects can be felt up to 45 minutes later and can last for several hours.

It can take days for someone to feel normal again after consuming cannabis.

Long after the drug was first consumed and the ‘high’ has worn off, cannabis use remains detectable by a drug test.

Drug testing methods that can be used to detect cannabis use include oral fluid (saliva) drug testing, urine drug testing, hair drug testing and nail drug testing.

What is the difference between THC and CBD?

Although both cannabidiol (CBD) and tetrahydrocannabinol (THC) derive from the Cannabis sativa plantand are classed as cannabinoids, there are some differences between the two.

THC is the main psychoactive ingredient found in cannabis and is responsible for the ‘high’ that people experience when using cannabis.

Unlike THC however, CBD produces few if any psychoactive effects.

THC that is used recreationally or for non-medical purposes is illegal in Ireland and is controlled under the Misuse of Drugs Act 1977. However, CBD products are legal in Ireland – albeit subject to heavy regulation.

For CBD products to be legally bought and sold in Ireland, they must be hemp-derived and contain less than 0.2% (trace levels) of THC.

When used in medical settings, both THC and CBD can be prescribed to treat certain conditions including epilepsy, multiple sclerosis (MS), and nausea and vomiting in adults undergoing chemotherapy, where other treatments have previously failed or been unsuitable.

Where can I buy a drug test?

Our Home Drug Testing Kit has been designed to give you peace of mind or enable you to seek support for a friend or loved one who is struggling with substance misuse.

This easy-to-use, self-contained screening kit can detect drugs and their metabolites in a urine sample, with built-in test strips that allow you to read the results in just 5 minutes

Please be aware that our home drug test kits are for peace of mind only, and the results cannot be used in court. If you require a drug test for official matters, you will need a legally-instructed drug test.

For confidential advice about which test might best suit your needs, you can also call our Customer Services team on 01 402 9366 or email

Home Drug Testing Kit

Buy your easy-to-use home drug test kit online now for just €20.

Marie Law AlphaBiolabs

Marie Law

Head of Toxicology at AlphaBiolabs

A highly-skilled and respected scientist with over 13 years’ experience in the field of forensics, Marie joined AlphaBiolabs in 2022 and oversees the company’s growing toxicology team.

As Head of Toxicology, Marie’s day-to-day responsibilities include maintaining the highest quality testing standards for toxicology and further enhancing AlphaBiolabs’ drug and alcohol testing services for members of the public, the legal sector, and the workplace sector.

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