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Chemical structure of the tricyclic
antidepressant amitriptyline
Tricyclic antidepressants are a class of antidepressant drugs first used in the 1950s. They are named after the drugs' molecular structure, which contains three rings of atoms (compare tetracyclic antidepressant). The term 'tricyclic antidepressant' is sometimes abbreviated to TCA.
Most tricylic antidepressants work by inhibiting the re-uptake of the neurotransmitters norepinephrine and serotonin by nerve cells. They are not considered addictive and have many fewer side-effects and restrictions than the MAOIs. For many years they were the first choice for pharmacological treatment of depression. Although they remain effective, they have been increasingly replaced by SSRIs and other newer drugs. These newer antidepressants are thought to have fewer side effects and are also thought to be less effective if used in a suicide attempt, as the treatment and lethal doses are much further apart than with the tricyclic antidepressants. The reason why tricyclic antidepressants are still used is their high potency, especially in severe cases of clinical depression.
Tricyclics are also known as effective analgesics for different types of pain, especially neuropathic or neuralgic pain (like back pain in radiculitis). A precise mechanism for their analgesic action is unknown, but it is thought that they modulate anti-pain opioid systems in CNS via indirect serotonergic route. They are also effective in migraine prophylaxis, but not in abortion of acute migraine attack. The mechanism of their anti-migraine action is also thought to be serotonergic.
The side effects of tricyclic antidepressant may include drowsiness, anxiety, restlessness, dry mouth, constipation, urinary retention or difficulty with urination, cognitive and memory difficulties, weight gain, sweating, dizziness, hypotension, akathisia, decrease in sexual ability and desire, muscle twitches, weakness, nausea, increased heart rate and irregular heart rhythms (rare). Some of these side effects relate to their anticholinergic properties.
It is worth noting that many people suffer few, if any, side effects from taking tricyclic antidepressants. However, as with any medication, it is always worth reporting any problems you encounter to your health care provider.
The first tricyclic antidepressant discovered was imipramine, which was discovered accidentally in a search for a new antipsychotic in the late 1950s.
Antidepressant drugs in the tricyclic drug group include:
- amitriptyline (Elavil®, Endep®)
- amoxapine (Asendin®)
- clomipramine (Anafranil®)
- desipramine (Norpramin®, Pertofrane®)
- dothiepin hydrochloride (Prothiaden®, Thaden®)
- doxepin (Adapin®, Sinequan®)
- imipramine (Tofranil®)
- lofepramine (Gamanil®, Lomont®)
- nortriptyline (Pamelor®)
- protriptyline (Vivactil®)
- trimipramine (Surmontil®)