Marijuana and memory

Marijuana affects the part of the brain which is responsible for memory. It affects many functions within the brain but the ability to recall or recognise is particularly hard hit.

This is why prolonged use of marijuana has a detrimental effect on someone’s performance at school or work.


Memory is the name given to a series of processes within the brain which controls your ability to store, retain and retrieve information. This includes experiences as well.

There are 3 types of memory:

  • Sensory memory
  • Short term memory
  • Long term memory

Sensory memory is the earliest and instantaneous process in which information is stored for only a few seconds, e.g. 3 seconds at a time. Some of this information is passed onto short term memory. Short term memory is known as ‘working memory’ and is the memory we constantly use or are aware of. Information is stored here for only a short space of time, e.g. 20 seconds before being passed into the long term memory.

Long term memory is the process of storing information on a continual basis. It is a memory you are largely unaware of but can call upon if needed, e.g. some long forgotten piece of information.

The hippocampus, amygdala and the striatum are involved in these processes.

So how does marijuana affect your memory?

Marijuana and the hippocampus

The hippocampus is a section within the medial temporal lobe (side of the brain) of the brain. It is part of the limbic system - a set of structures within the brain which control memory, emotions and a sense of smell.

It plays an important part in memory and spatial awareness which is why both of these are impaired when someone uses marijuana. The primary chemical in marijuana is tetrahydrocannabinol (THC) which affects these functions to the extent that balance and co-ordination are impaired. Plus it becomes difficult to recall past events.

Basically, your reactions slow down and you find you take longer to think and act than normal.

This is why it is not a good idea to drive or engage in any activity which requires an instant decision.

Memory, thinking, decision making, judgement and learning are all affected which is even more of a problem the longer you use marijuana.

It is important to realise that the hippocampus becomes less effective over time. Neurons die over a period of time and are not replaced which is a normal part of the ageing process.

This means that it is harder to learn new information.

But THC’s in marijuana may speed up this loss which reduces the effectiveness at which someone learns or processes new information.

Can this be reversed?

If someone stops using marijuana their cognitive abilities such as learning, may return to normal but this may apply to short term use only.

More research is needed into the long term effects of marijuana on certain brain functions, e.g. memory.

Marijuana and Alzheimer’s disease

Research undertaken by Ohio University suggests that small doses of marijuana may help to stave off Alzheimer’s disease.

The popular view is that marijuana causes memory loss but this study argues that it may improve memory and even cause new brain cells to grow. It may also reduce inflammation within the brain which is known to cause memory problems.

(Source: Daily Telegraph: Science News: Nov 2008)

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