Tricyclics were discovered after a series of accidental break throughs by scientists in the late 1950s.
The name is a result of their three wheeled molecular structure.
They are very strong and rarely prescribed for depression today, unless all other options have been exhausted.
This is because, with tricyclics being so potent, it is quite easy for the patient to overdose.
Obviously, in a person who may already have suicidal tendencies, ease of a fatal overdose is an undesirable quality for a treatment.
Tricyclics have a dual effect on the body's central nervous system.
The drug prevents the reuptake of noradrenaline and serotonin, which means the levels will rapidly increase.
These are the feel good chemicals, yet the full effects of tricyclics are not felt by the patient for several weeks.
This means that the drugs must also cause longer term alterations in the brain, specifically in the areas responsible for emotions and higher functioning such as the hippocampus and the cortex.
The side effects of this type of antidepressant can be unpleasant.
Tricyclics can lead to fatigue, constipation, increased heart rate, bladder problems and blurred vision.
This is another reason why tricyclics are generally only prescribed to a depressed patient of their condition is severe and they have had little success with other treatment options.
Before tricyclics are prescribed a patient will probably have been given MAOIs (monoamine oxidase inhibitors) and SSRIs (selective serotonin reuptake inhibitors).
If you are suffering from depression, you should book an appointment with your family doctor who will be able to talk you through all the available treatment options.
As well as medication, sufferers might also benefit from counselling or cognitive behavioural therapy.