Effects of recreational drugs

• Heroin highly addictive opiate recreational drug taken for euphoric high
• Heroin has depressant effects of the central nervous system- it slows down activity 
• Heroin is injected intravenously and flows through bloodstream to the brain. Once in the brain is is broken down into morphine 
• Morphine binds to specific opiate receptors at the synapse, cerebral cortex, limbic system and hypothalamus.
• Receptors for heroin/morphine exist in the body because the Central Nervous System has its own opioid system 
• Endorphins and enkephalins are the bodies natural painkillers. Heroin takes advantage of this system by binding with the natural opioid receptors to enhance its effects
• Heroin is an agonist drug because it mimics the action of another chemical
• Heroin binds to the natural opioid receptors because it has a complimentary shape
• Repeated heroin use leads to down regulation 
• Regular use means the opioid receptors on the post synaptic neurons are constantly binding with the morphine molecules 
• repeated heroin use desensitises the receptors to the effect of the drug
• Desensitisation means that more of the drug is needed to have the same effect- tolerance
• Cocaine is an illegal and addictive drug. It is taken recreationally for its stimulating effects; it speeds up the body e.g. heart rate
• Users of cocaine experience a 'come down' after taking it due to depleted levels of dopamine and the bodies need to recover.
• Cocaine works on the reward pathway and dopamine receptors in the brain.
• Cocaine draws on the idea that there is reuptake by the presynaptic neuron of neurotransmitter left in the synaptic gap.
• Cocaine blocks the binding site on the reuptake receptor, or transporter molecule, and stops the reuptake of dopamine back into the presynaptic neuron.
• with cocaine blocking the reuptake of dopamine there is excess dopamine in the synapse because it is not being reabsorbed.
• This excess of dopamine due to cocaine leads to over-stimulation at the postsynaptic receptors.
• Therefore there is more dopamine than usual creating intense feelings of pleasure, or euphoria.
• The continuous binding of dopamine to the dopamine receptors is overstimulating and negatively affects the neural transmission.
• Overtime with repeated cocaine use the dopamine receptors become damaged, changing shape which prevents neurotransmitters binding successfully.
• The number of dopamine receptor sites will also decrease.

  This leads to desensitisation and more dopamine is required to stimulate the post synaptic neuron to a 'normal level'.
• As there is a loss of response to the drug so more is needed to experience the same effect, this is called tolerance.
• A person becomes addicted because they crave the intense pleasure experienced, due to activation of the dopamine reward pathway, and therefore want to take the drug again because it is rewarding.