What Do You Know About How Antidepressants Work?


Antidepressants are a type of medication used to treat clinical depression or prevent it recurring. They can also be used to treat a number of other conditions, including:

  • Obsessive-compulsive disorder (OCD);
  • Generalized anxiety disorder;
  • Post-traumatic stress disorder (PTSD).

While antidepressants can treat the symptoms of depression, they don’t always address its causes. This is why they’re usually used in combination with therapy to treat more severe depression or other mental health conditions caused by emotional distress.

Types of antidepressants

There are several different types of antidepressants, including:

  • Selective serotonin reuptake inhibitors (SSRIS);
  • Serotonin and norepinephrine reuptake inhibitors (SNRIS);
  • Tricyclics and tricyclic-related drugs;
  • Monoamine oxidase inhibitors (MAOIS);
  • Other antidepressants.

They all tend to act on the same brain chemicals and cause similar effects, but the different types have different chemical structures and may have different side effects.

How antidepressants work

All antidepressants work in a similar way, though there are various types of antidepressants—often called “families”—that each work a bit differently. They all, however, increase the brain’s concentration of various neurotransmitters.

Tricyclic antidepressants (TCAs)

These increase both norepinephrine and serotonin concentrations.

  • They’re the oldest type of antidepressant, first developed in the 1950s.
  • They work by prolonging the action of noradrenaline and serotonin in the brain.
  • They’re called ‘tricyclic’ because of their chemical structure, which has 3 rings.
  • They tend to cause more unpleasant side effects compared with other types of antidepressants.

Tricyclic-related drugs:

  • They act in a very similar way to tricyclics, but they have slightly different chemical structure.
  • They tend to cause more unpleasant side effects compared with other types of antidepressants, but they’re less likely to cause antimuscarinic effects than tricyclics.

Monoamine oxidase inhibitor antidepressants (MAOIs)

They include medicines like:

  • Phenelzine;
  • Isocarboxazid;
  • Moclobemide.

About MAOIs:

  • They work by making it harder for an enzyme (monoamine oxidase) that breaks down noradrenaline and serotonin to do its job, causing these chemicals to stay active in the body for longer.
  • They can have dangerous interactions with some kinds of food, so when taking MAOIs you need to follow a careful diet.
  • Because of these interactions, you’re not likely to be prescribed a MAOI unless you’ve tried all other types of antidepressant and none of them have worked for you.
  • They should only be prescribed by specialists.

Side effects often associated with TCAs and MAOIs include:

  • Drowsiness;
  • Weight gain;
  • Dry mouth;
  • Constipation;
  • Blurred vision;
  • Dizziness;
  • Sexual dysfunction.

Because of these side effects, doctors will usually prescribe a newer antidepressant first. In some people, newer medications don’t work as well as the older medications.

Selective serotonin reuptake inhibitors (SSRIs)

The most commonly prescribed group of antidepressants is selective serotonin reuptake inhibitors (SSRIs), including:

  • Fluoxetine;
  • Paroxetine;
  • Fluvoxamine;
  • Sertraline;
  • Citalopram.

About SSRIs:

  • They were first developed in the late 1980s, so they have been in use for about 30 years.
  • They work by blocking the re-uptake of serotonin into the nerve cell that released it, which prolongs its action in the brain.
  • The side effects SSRIs can cause are generally easier to cope with than those of other types of antidepressants.
  • They’re the most commonly prescribed type of antidepressant in the UK.

The main action of SSRIs is to increase the concentration of serotonin. In fact, SSRIs fail to work for mild cases of depression, suggesting that regulating serotonin might be an indirect treatment only.

Serotonin-norepinephrine reuptake inhibitor (SNRI)

The antidepressant venlafaxine is described as a serotonin-norepinephrine reuptake inhibitor (SNRI). It increases serotonin and norepinephrine concentrations.

  • The first of these was developed in the early 1990s, so they’re one of the newer types of antidepressant.
  • They’re very similar in action to SSRIs, but they act on noradrenaline as well as serotonin.
  • They have a more selective action than tricyclics, which means they’re better at targeting the brain chemicals which affect your mood without causing unwanted side effects by affecting other chemicals and other parts of the body as well.
  • They’re sometimes preferred for treating more severe depression and anxiety.

As a side note: antidepressants are prescribed to treat and manage other illnesses. TCAs, for example, have local anesthetic-type properties and have been used to treat chronic pain due to nerve injury. SSRIs, on the other hand, are commonly prescribed to treat various anxiety disorders that share a common underlying cause involving serotonin.

Hello Health Group does not provide medical advice, diagnosis or treatment.

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