agonist and antagonist substitution

• one common treatment for addiction is medication, typically given to people with substance use addiction, these drugs work at the level of the synapse to alter behaviour.
• 2 main types of biological treatments:

  1. agonist drugs are chemicals that bind to the postsynaptic receptor - they imitate the action of a synthetic chemical such as heroin.
  2. antagonist drugs bind to a receptor but rather than causing a reaction, it blocks the action of a particular substance
• agonist substitution

  methadone is a drug that is most commonly used as a treatment for opioid addiction, particularly heroin, as it acts as a synthetic replacement for heroin.

  it occupies the dopamine receptors in the brain, thus mimicking the effect of heroin minus the "high."
• agonist substitution

  because it reduces withdrawal symptoms, but does not give the same euphoric rush associated with heroin, methadone patients do not experience the uncontrolled compulsive and disruptive behaviours associated with heroin users.
• agonist drugs

  also, because it is given orally, the blood concentrations of the methadone will rise and fall slowly, compared with the rush and crash of heroin which is injected.
• antagonist substitution

  while methadone is used to manage the symptoms of withdrawal, naltrexone is used to prevent recovering addicts from relapsing.
• antagonist substitution

  naltrexone occupies dopamine receptors but does not activate them.

  this means that if a patient who has taken naltrexone were to take an opioid such as heroin, they would not experience a "high" or pleasure because the dopamine receptors are blocked, making the drug less rewarding.
• antagonist substitution

  naltrexone is often offered alongside psychological counselling to help prevent the risk of relapse.

  it can be used for up to six months - however, the addict has to overcome the symptoms of withdrawal before this can happen.
• antagonist substitution

  because it blocks the dopamine receptors, thus preventing activation of the mesolimbic pathway, naltrexone is starting to be used for other addictions, such as alcohol or gambling