A Showdown between Tricyclic Antidepressants and SSRI Antidepressants
Posted 04-06-2008 at 03:39 PM by ladypam
I once encountered someone asking the difference between tricyclic antidepressants (TCAs) and selective serotonin reuptake inhibitor (SSRI) antidepressants since both are antidepressants and both function to prevent serotonin from entering the nerve cell. So where lies the difference?
Although both are classified under antidepressants, they both are composed of different substances and have different ways of inhibiting serotonin from entering the neuron. They also have different side effects and effectiveness.
SSRI agents act on the reuptake of serotonin. Looking at this mechanism at a microscopic level, nerve cells function as relay bridges to signal or send reactions from one organ to another. Between the nerve cells is a synaptic or a gap where neurotransmitters such as serotonin are released and received by the connecting nerve cells. The nerve cell releasing the neurotransmitters is the presynaptic cell while the cell receiving is the postsynaptic cell. When neurotransmitters are released by the presynaptic cell only a tenth get recognized by receptors found in the surface of the postsynaptic cell. The remaining nine-tenths are taken back the presynaptic cell through the process of reuptake.
It is thought that with depression, the postsynaptic cell is having problems taking up the serotonin or with stimulating the neuron, thus no transmission of signals occurs. With SSRIs, the serotonin levels are left in the synapse for a longer period of time since their uptake is inhibited. Therefore, the postsynaptic cells are able to sense the serotonin and become stimulated to fully activate its receptors to take up the serotonin. The process doesn’t stop here since the body has regulating systems to detect changes from its normal processes such as an increase in serotonin. When serotonin levels increase, it also activates receptors in the presynaptic cell that stops the production of serotonin. It also regulates the number of post synaptic receptors to modify the ratio of serotonin with its receptor. Because of this, a greater percentage of serotonin receptors get activated and thus restoring normal signal transmission between nerve cells.
But what does all these processes and regulations reflect in terms of what the patient feels? This actually explains why full relief from depression does not happen at once but after several weeks since it has to adapt the body to a change in these regulatory processes that govern serotonin levels.
With Tricyclic antidepressants, which incorporate three rings into its chemical structure, the mechanism is slightly different. Although they also inhibit the uptake of serotonin in the nerve gaps, it also affects other neurotransmitters that are activated by monoamine oxidase enzymes such as norepinephrine. Tricyclics are able to inhibit these substances by attaching to the transporter protein in the membrane of the postsynaptic cell in an area adjacent to where the neurotransmitter has bound itself. This binding locks the neurotransmitter in place, thus preventing its uptake into the presynaptic cell.
Tricyclics are also attracted to the histamine and muscarinic receptors, therefore attaching to them as well and creating an increase in histamine in the blood. These substances create a sedative effect on the patient.
Another point of comparison between TCAs and SSRIs is their selectivity. SSRIs are known to be selective only to serotonin and its receptors therefore limiting the side effects that it produces on the patients. However, TCAs generally affect several receptors including norepinephrine and histamine. Because of this lack of selectivity, they tend to produce varying side effects from the interplay of these increased substances in the body.
The side effects produced by SSRI normally include nausea, diarrhea, vomiting, headache, drowsiness, dizziness, grinding and clenching of teeth, vivid dreams, a change in appetite, a change in weight, tremors, sweating, impairment in liver and kidney functions, alterations in sexual behavior, thoughts of suicide and an increase in sunburn risk. These side effects may be accounted for the increase in serotonin levels in the body and its way of adapting to it. These side effects usually go away as the real antidepressive changes occur. Take note that the occurrence of these side effects depend on the person’s ability to adapt to the changes made by SSRI. This is the reason why small doses are given at first to test the reaction of the body to the medication. Some patients are also seen to produce mania as a side effect, especially those diagnosed with a slight bipolar disorder.
There are no major or severe cardiovascular effects from the use of SSRIs. They only affect the calcium, potassium, and sodium channels in vascular and cardiac muscles by inhibiting them. SSRIs are also known to not produce addiction although when its medication is stopped abruptly, it can bring about withdrawal symptoms psychological and somatic, sometimes described as having their brains zapped. These symptoms may last from weeks to several months.
On the other hand, the side effects of TCAs include having a dry mouth and nose since the salivary glands are affected, a decrease in the motility of the gastro intestinal tract leading to constipation, problems with urination, an increase in temperature, and blurred vision from an effect in the ability of the eyes to accommodate. These effects usually go away as the body gets used to the TCAs. It can also have nausea, drowsiness, restlessness, anxiety, difficulty in memory and cognitive skills, hypersensitivity, weakness, a decrease in the ability and desire for sexual relations, and hypotension. TCA also affects the cardiovascular system by producing a higher risk for irregular cardiac rhythms and tachycardia.
An important point of comparison for these two substances is their toxic doses. SSRIs have a high toxic dose therefore making it a good choice to avoid suicide through overdose. On the other hand, TCAs have a low toxic dose, therefore having a high risk for overdose. In fact, there are many cases of suicide attempts through ingesting several TCA s at once.
TCAs and SSRIs have both been effective in the treatment of depression. The decision on which one to choose will lie on your symptoms and the ability of your body to accept and react to these substances. If you are suffering from depression, talk to your doctor on the options that are open to you and decide on which one to take.
Although both are classified under antidepressants, they both are composed of different substances and have different ways of inhibiting serotonin from entering the neuron. They also have different side effects and effectiveness.
SSRI agents act on the reuptake of serotonin. Looking at this mechanism at a microscopic level, nerve cells function as relay bridges to signal or send reactions from one organ to another. Between the nerve cells is a synaptic or a gap where neurotransmitters such as serotonin are released and received by the connecting nerve cells. The nerve cell releasing the neurotransmitters is the presynaptic cell while the cell receiving is the postsynaptic cell. When neurotransmitters are released by the presynaptic cell only a tenth get recognized by receptors found in the surface of the postsynaptic cell. The remaining nine-tenths are taken back the presynaptic cell through the process of reuptake.
It is thought that with depression, the postsynaptic cell is having problems taking up the serotonin or with stimulating the neuron, thus no transmission of signals occurs. With SSRIs, the serotonin levels are left in the synapse for a longer period of time since their uptake is inhibited. Therefore, the postsynaptic cells are able to sense the serotonin and become stimulated to fully activate its receptors to take up the serotonin. The process doesn’t stop here since the body has regulating systems to detect changes from its normal processes such as an increase in serotonin. When serotonin levels increase, it also activates receptors in the presynaptic cell that stops the production of serotonin. It also regulates the number of post synaptic receptors to modify the ratio of serotonin with its receptor. Because of this, a greater percentage of serotonin receptors get activated and thus restoring normal signal transmission between nerve cells.
But what does all these processes and regulations reflect in terms of what the patient feels? This actually explains why full relief from depression does not happen at once but after several weeks since it has to adapt the body to a change in these regulatory processes that govern serotonin levels.
With Tricyclic antidepressants, which incorporate three rings into its chemical structure, the mechanism is slightly different. Although they also inhibit the uptake of serotonin in the nerve gaps, it also affects other neurotransmitters that are activated by monoamine oxidase enzymes such as norepinephrine. Tricyclics are able to inhibit these substances by attaching to the transporter protein in the membrane of the postsynaptic cell in an area adjacent to where the neurotransmitter has bound itself. This binding locks the neurotransmitter in place, thus preventing its uptake into the presynaptic cell.
Tricyclics are also attracted to the histamine and muscarinic receptors, therefore attaching to them as well and creating an increase in histamine in the blood. These substances create a sedative effect on the patient.
Another point of comparison between TCAs and SSRIs is their selectivity. SSRIs are known to be selective only to serotonin and its receptors therefore limiting the side effects that it produces on the patients. However, TCAs generally affect several receptors including norepinephrine and histamine. Because of this lack of selectivity, they tend to produce varying side effects from the interplay of these increased substances in the body.
The side effects produced by SSRI normally include nausea, diarrhea, vomiting, headache, drowsiness, dizziness, grinding and clenching of teeth, vivid dreams, a change in appetite, a change in weight, tremors, sweating, impairment in liver and kidney functions, alterations in sexual behavior, thoughts of suicide and an increase in sunburn risk. These side effects may be accounted for the increase in serotonin levels in the body and its way of adapting to it. These side effects usually go away as the real antidepressive changes occur. Take note that the occurrence of these side effects depend on the person’s ability to adapt to the changes made by SSRI. This is the reason why small doses are given at first to test the reaction of the body to the medication. Some patients are also seen to produce mania as a side effect, especially those diagnosed with a slight bipolar disorder.
There are no major or severe cardiovascular effects from the use of SSRIs. They only affect the calcium, potassium, and sodium channels in vascular and cardiac muscles by inhibiting them. SSRIs are also known to not produce addiction although when its medication is stopped abruptly, it can bring about withdrawal symptoms psychological and somatic, sometimes described as having their brains zapped. These symptoms may last from weeks to several months.
On the other hand, the side effects of TCAs include having a dry mouth and nose since the salivary glands are affected, a decrease in the motility of the gastro intestinal tract leading to constipation, problems with urination, an increase in temperature, and blurred vision from an effect in the ability of the eyes to accommodate. These effects usually go away as the body gets used to the TCAs. It can also have nausea, drowsiness, restlessness, anxiety, difficulty in memory and cognitive skills, hypersensitivity, weakness, a decrease in the ability and desire for sexual relations, and hypotension. TCA also affects the cardiovascular system by producing a higher risk for irregular cardiac rhythms and tachycardia.
An important point of comparison for these two substances is their toxic doses. SSRIs have a high toxic dose therefore making it a good choice to avoid suicide through overdose. On the other hand, TCAs have a low toxic dose, therefore having a high risk for overdose. In fact, there are many cases of suicide attempts through ingesting several TCA s at once.
TCAs and SSRIs have both been effective in the treatment of depression. The decision on which one to choose will lie on your symptoms and the ability of your body to accept and react to these substances. If you are suffering from depression, talk to your doctor on the options that are open to you and decide on which one to take.
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