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How tricyclic antidepressants work

Posted Apr 02 2009 12:53pm
If you haven't read a preface, I'd strongly recommend you to look through it: Part 1, 2, 3.


What are the tricyclics used for ?
Tricyclic antidepressants are used to improve mood in people who are feeling low or depressed. The tricyclics may also be used to help the symptoms of anxiety and a number of other symptoms. The tricyclics are the most commonly prescribed antidepressants but there are many other antidepressants. All these drugs seem to be equally effective at the proper dose but have different side effects to each other. If one drug does not suit you, it may be possible to try another.

How do the tricyclics work ?
The brains has many naturally occurring chemical messengers. Two of these are called serotonin (sometimes called 5-HT) and noradrenaline. Both are important in the areas of the brain that control or regulate mood and thinking. It is known that these two chemical messengers are not as effective or active as normal in the brain when someone is depressed. Tricyclic antidepressants increase the amount of these chemical messengers in the brain. This can help correct the lack of action of these messengers and help to improve mood. The tricyclics can also effect another chemical in the brain called "acetylcholine" and this is the cause of some of their side-effects.

"Reduced" nerve activity but with recycling blocked, and increased messages passes:

Some antidepressants e.g. the tricyclics and venlafaxine, block the reuptake of serotonin and noradrenaline.
Unfortunately, these antidepressant drugs also affect other transmitter systems e.g. acetylcholine, dopamine, histamine etc. Some are a bit like "blunderbuss" treatments i.e. they hit the part that seems to be wrong, but also hit lots of other parts which aren't wrong. The side effects you get from drugs are from these extra "hits". The amount that these drugs effect different transmitters varies between drugs and is the reason you get slightly different side effects from each of the different drugs. These can include:

- If you block acetylcholine receptors, it may blunt your reactions, can produce mild sedation and confusion etc. as well as producing a dry mouth, blurred vision etc.
- Affecting your noradrenaline may also sometimes upset your blood pressure e.g. you may feel dizzy when you stand up etc.
- Too much serotonin and you may feel sick, less hungry, get headaches or migraines
If you block histamine receptors, it can make you feel drowsy (just the same as if you take an antihistamine tablet such as "Piriton" for hay fever or allergy).


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