Heroin

• Heroin is a highly addictive opiate drug. It is taken recreationally for a euphoric ‘high’.
• Heroin has depressant effects on the CNS – it slows down activity, including neurons involved in pain. This is

  why opiates are valued as analgesics (painkillers).
• Heroin is usually injected intravenously and flows through the bloodstream to the brain. Once in the brain it is broken down into morphine (a closely related opioid).
• Morphine binds to specific opioid receptors at the synapse - (mu) receptors in the cerebral cortex, limbic system and hypothalamus. This releases dopamine (feelings of pleasure)
• Receptors for heroin/morphine exist in the body because the CNS 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, i.e. it binds to the natural opioid receptors because it has a complimentary shape, thus increasing the levels of dopamine.
• Endorphin and morphine have a similar shape so can bind to the same opioid receptors in the brain
• long term effects of heroin : Repeated heroin use leads to down-regulation, Regular use means the opioid receptors on the postsynaptic neuron are constantly binding with morphine molecules, This desensitises the receptors to the effect of the drug, Therefore more of the drug is needed to have the same effect – tolerance.