Tricyclic antidepressants (TCA) and selective serotonin reuptake inhibitors (SSRIs) are both groups of medications used for the treatment of clinical depression. TCA are older drugs and SSRIs have taken over, since they are more easily tolerated and safer when overdosed. Main differences are noticed in mechanism of action and side effects these drugs cause.
These drugs are similarly efficient when it comes to the treatment of depressive disorders. About 60% of all patients treated for major depression respond to the treatment to either of the drugs, and both medications are proven to cause about 30% higher response than placebo.
TCA and SSRI - Mechanism of Action
Scientist discovered that the brain of the person suffering from depression lacks certain substances (neurotransmitters). Because of that fact, the treatment for depression is focused on elevation and prolonged effects of the neurotransmitters in the brain, such as serotonin and norepinephrine.
TCAs work by slowing the reabsorption of the serotonin and norepinephrine. These drugs also affect some other receptors, like alpha1 adrenergic, histaminic and cholinergic receptors and these effects are responsible for many unwanted side effects.
On the other hand, SSRIs are strong inhibitors of the serotonin reuptake and work little on inhibition of norepinephrine. Since these drugs are more selective than TCAs, there is also a lower incidence of side effects.
Adverse Effects of TCAs and SSRIs
As we already stated, there are much more side effects asociated with tricyclic antidepressants than with selective serotonin reuptake inhibitors.
TCAs affect cholinergic receptors and thus cause antiholinergic effects. Thes einclude: sedation, dry mouth, constipation, retention of urine, diziness and vision problems. Other problems that may arise in patients using TCAs are: weight gain, orthostatic hypotension (the person may feel dizzy when changing posture rapidly) and cardiotoxicity, which may be present even in therapeutic doses of the presribed drug. Older patients may experience an increased risk of undetected cardiac function problems, and TCAs may not be so useful in these patients. Sedation may also be an important issue, disabling people in performing normal everyday activities in some cases.
SSRIs are not known to cause sedation, antichlinergic effects, otrhostatic hypotension or toxic effects to the human heart. Patients using SSRIs may complain about nausea, diarrhea, headaches, sleeping problems, agitation, tremor or dizziness. These drugs also affect the sexual function of the treated patients. Most of the side effects caused by SSRIs subside after some time.
Patients who overdosed TCAs may experience problems in the functioning of the brain and the heart, such as rapid heartbeat agitation, flushed face, confusion, seizures and cardiorespiratory collapse. This condition may be lethal and requires urgent medical assistance.
SSRIs overdose doesn’t affect the heart and doesn’t cause seizures, coma or some other severe medical consequences.