❝ in the main drugs either excite or block receptors ❞

To understand how drugs work is to understand receptors. We are concerned with 'psychoactive' drugs - drugs that have an effect on thoughts, feelings and mood.


The body has many different receptors which are built into all kinds of cells. Receptors make things happen: for example activating muscle receptors causes muscle contraction, receptors on glands cause secretions from the gland, and in the brain they cause thoughts and feelings to happen. As far as addiction is concerned it is the brain receptors that are most important. Most psychoactive drugs affect only a small number of receptor types.

Normally receptors are activated by the body's own chemicals called neurotransmitters. These chemicals are released from one cell and activate receptors at neighbouring cells. This is the brain's communication system. The brain is estimated to have 86 billion cells each sending signals to many other cells. It is indeed a remarkable structure.

What do drugs do?

Drugs have many different effects. Here we are thinking of psychoactive drugs which can be thought of as either activating or blocking receptors. Drugs typically have an effect on several different receptors and this is generally a good thing for recreational drug use in that it softens the impact of the drug. The opposite is true for medicines where pharmaceutical companies try to find drugs with very specific effects in order to minimise side effects and maximise the desired medical use of the drug.

Slideshow: if you are interested in the science, take a look at the slideshow. It will take an hour to go through all the slides so get comfortable and give yourself plenty of time to digest the learning points, or you might want to have more than one sitting to take it all in.

[Best to view full screen]

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The Drug Classroom 

is an excellent collection of short video presentations about the effects and mode of action of commonly used drugs.