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Summary Drug Functions and Mechanisms
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All drug types and their symptoms summarised. Their structure and groups are also discussed. Associated disorders discussed
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Chapter 15 – Drug use, drug addiction and reward circuitsGlobally:
- Over 1 billion people are addicted to nicotine
- 76 million are addicted to alcohol
- 40 million are addicted to illegal drugs
Basic principles of drug action – administration, absorption, and penetration of the CNS
Oral Ingestion Injection Inhalation Mucous membrane
Dissolve in the Injections act fast and Capillaries in the lungs Snorting drugs
stomach acid. They are very strong. can pass drugs
flow to the large Subcutaneous (into through the
intestine, then are fatty tissue under bloodstream.
absorbed into the skin), intravenous Anaesthetics are given
blood (into veins), or this way.
intramuscular.
It can take a while for Bloodstream delivers Can cause lung Suppositories and
effects to settle in, but drug right to the brain damage and enemas (in the bum)
it is safer than any when drug is administration is
other method of administered through random, so hard to
ingestion the vein. Hard to track
counteract overdose
or allergy if drug is
taken this way
Drug action, metabolism, and elimination
The blood-brain barrier prevents harmful chemical substances from entering the CNS near the glial
cells and neuronal structures. The drugs are carried to the CNS by blood vessels, but they cannot
intrude into the deeper systems.
Some drugs act by diffusing through the blood and having depressant effects, like anaesthetics,
whilst other drugs, like morphine, bind to receptors and manipulate synthesis, storage, and release.
Drug action is eliminated through enzymes synthesised in the liver. The drugs are metabolised into
less harmful forms, which are then excreted or sweated out of the skin. Sometimes, the drugs are
metabolised to the point where they cannot pass through lipid membranes, preventing entry to the
brain and slowly, the effect wears off.
Half-life of a drug is the amount of time taken for a drug in your system to reach half the initial
amount – important, as you cannot quit cold turkey, since the drug remains in you, and you desire
more. It also takes a while for drugs to metabolise, so you cannot risk taking more when you are still
filtering out earlier doses.
Drugs with a long-half life are likely to make the user suffer less withdrawal symptoms. This is
because they take longer to kick in, and they last longer, so more doses are not frequently needed to
stay high.
If a drug has a half life of 60 minutes at a dose of 100mg, then
, - 50mg left are 60 mins
- 25 mg left are 120 mins
- 12.5mg left after 180 mins etc
Takes at least 5-6 half lives for a drug to be considered out of the system
Drugs with a short half life are cocaine, heroin, and paracetamol.
Drugs with a long half-life are methadone, MDMA, and Xanax.
Drug tolerance, withdrawal, and dependence
Tolerance: decreased sensitivity to a drug after repeat exposure. Habituation. More of the drug is
needed to achieve the desired effect. Cross tolerance is when drugs in the same class, that act in the
same way, cause tolerance in a person. Sensitivity to a drug may increase, where there is loss in the
effect one part of the drug has, so someone takes more, which worsens other side effects. Someone
may stop feeling sick, but still have stomach pains from a drug. They think they are tolerant, so they
take higher doses, which worsens stomach pain. Drugs do not just attack, our bodies try to respond
to the drugs, tolerance becoming a thing when our bodies are basically numb to the dosage.
When someone is trying to detox, they should resort to using long-half life drugs at slightly smaller
doses each time, otherwise their tolerance will make it, so they go into withdrawal upon immediate
recall of the drug.
Metabolic tolerance: drug tolerance increases due to reduced amount of the drug getting to the
active site (not enough drug at the site). Also, the drug gets metabolised much more quickly, causing
the effects to be short lasting.
Functional tolerance: Reduction in drug reactivity at the site of drug (body does not respond to drug
like it used to; it adapted to it). Tolerance to psychoactive drugs is usually a functional tolerance.
Neural circuits are affected by this drug use, causing receptors to decrease with binding efficiency,
making the body realise that the drug is something naturally occurring (it is not, but it treats it as
such).
Sudden drug elimination leads to withdrawal. They usually have the opposite effect to the actual
drug. Anticonvulsants can cause seizures upon withdrawal and stopping the intake of
benzodiazepines causes insomnia.
People who suffer terrible withdrawal to a drug are said to be physically dependent on it.
The body has compensatory responses to tackle drug use, so taking these drugs away suddenly,
without allowing the body to realise that the drugs were taken away, causes the body to attack itself
an crave the drug to counteract this attack.
The longer the exposure, the greater the dose, the more sudden the elimination, the stronger the
severity of withdrawal.
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