News, views and top stories in your inbox. Don't miss our must-read newsletter Sign up Thank you for subscribing We have more newsletters Show me See our privacy notice Invalid Email

Cannabis is the most popular illegal drug in the UK.

One in three Brits have tried a prohibited substance, be it marijuana or otherwise, and more than 20 per cent take recreational drugs regularly, according to a survey in the Guardian .

New figures released by police in the West Midlands show a sizeable spike in cannabis usage in the region. And it's thought to be reflective of the country as a whole.

But few know what the class B drug actually does to the body – past bringing a sensation of feeling 'high'.

(Image: EyeEm)

When a person smokes a spliff, its active chemical Tetrahydrocannabinol (THC) travels through the body and effects the brain.

THC, the active chemical in cannabis, is stored in the fat cells, so takes longer to fully clear the body than any other common drug. The stronger the strain, the more THC it contains, and the longer it stays in the body.

Police use urine samples to test how much THC is in a person's body.

A review of data compiled by the US National Drug Court Institute estimated that:

• an occasional or first-time user would probably test positive up to four days after last using

• a frequent user would probably test positive up to 10 days after last using

• a very heavy user could test positive up to one to two months after last using

Long-term use of cannabis can increase the chances of depression and reduce motivation, the Birmingham Mail reports.

The drug affects the body in a number of ways. First, it changes the way the brain processes information.

(Image: AFP)

Marijuana contains at least 60 types of cannabinoids, which are chemical compounds that alter and fire on the brain's receptors.

The receptors keep neurons firing, magnifying thoughts, imaginationm and perception. Cannabis causes a high by boosting dopamine levels.

It can also cause anxiety, paranoia, and mood swings. And, like any drug, persistent use can lead to addiction.

Scientists say that just minutes after one drag on a spliff the heart rate speeds up by 20 to 50 beats per minute. This can last up to three hours.

Cannabis also makes blood vessels expand, which can lead to bloodshot eyes. It may also make pupils dilate.

Enough of the plant can lead to hallucinations. It also increases appetite – colloquially known as the 'munchies'.

A study on mice found the drug 'flips a switch' in the brain that is normally responsible for controlling appetite.

Chronic cannabis users, who light up at least three times a day, tend to have smaller grey matter volumes in the orbitofrontal cortex – which unsurprisingly is the part of brain tied to addiction.

But, interestingly, cannabis use was also linked with greater connectivity in the brain. There is evidence to suggest that the drug could help fight Alzheimer’s and dispelled the myth that smoking weed lowers IQ.