Marijuana and the brain

Marijuana contains a range of chemicals called the ‘cannabinoids’: but there is one chemical in particular known as ‘delta-9 tetrahydrocannabinol’ (THC) which has a direct effect on the brain.

This chemical crosses the blood-brain barrier and causes euphoria or a ‘high’ which occurs as a result of using marijuana.

Cannabinoid receptors

There are nerve cells within the brain which contain receptors known as ‘cannabinoid receptors’. These receptors are present in certain areas of the brain, namely those responsible for co-ordination, memory, sensory perception, movement, concentration and awareness of time and place.

These receptors are also present in the brain’s ‘reward system’.

The brain’s reward system is a series of regions which induces positive emotions such as pleasure as a means of regulating behaviours.

These regions control our responses to desired substances such as chocolate, desired actions such as sex and desired drugs such as marijuana.

They respond to these by releasing a chemical known as ‘dopamine’.

Dopamine is a neurotransmitter which is released as a response to a pleasurable experience such as using marijuana. This causes feelings of pleasure and enjoyment and a desire to repeat the experience.

This state of euphoria is more commonly known as a ‘high’.

Effects of THC’s on the brain’s reward system

This euphoric state is accompanied by other effects which include an altered perception of time, space and colour, increased appetite and a tendency to laugh and talk a lot.

These effects subside after a period of time to be replaced by a state of relaxation, drowsiness, tendency to withdraw from others and depression.

However, some people experience other effects which are less than pleasant. These include anxiety, panic attacks and paranoia. These often occur in inexperienced users or people who have ingested large amounts of marijuana or strong versions such as skunk or sinsemilla.

Hallucinations are another side effect and are more likely to occur if marijuana is eaten, e.g. a ‘hash cookie’, rather than smoked. The marijuana is consumed all at once and tends to be more potent than herbal cannabis.

Examples of this include paranoid delusions, disorientation and a poorly functioning memory. Many people find that they are unable to recall events or thoughts from their short term memory.

This is discussed in more detail in our marijuana and memory section.

These effects are magnified in people who have an anxious personality or are suffering from a mental illness. However more research is needed to determine if there is a link between marijuana and anxiety/depression.

These effects appear within minutes of smoking marijuana and last for 3 to 4 hours. They take longer to appear if marijuana is eaten but persist for a longer period of time.