What are antidepressants?
Antidepressants are a type of medicine used to relieve the symptoms of clinical depression, however, they do not always address its causes. This is why they're often prescribed along with a talking therapy such as cognitive behavioural therapy (CBT). They can also be used to treat several other conditions including obsessive compulsive disorder (OCD), generalized anxiety disorder, post-traumatic stress disorder (PTSD), eating disorders and chronic pain.
Antidepressants are not always recommended for treating mild depression because research has found limited effectiveness. However, antidepressants are sometimes prescribed for a few months for mild depression to see if any improvement in symptoms are experienced. If no benefits are experienced in this time, the medicine may be slowly withdrawn.
How do antidepressants actually work?
While it's not known exactly how antidepressants work, it is known that they affect levels of serotonin and noradrenaline, which are a type of chemical in the brain called a neurotransmitter. To understand how antidepressants work, it is essential to understand what neurotransmitters do.
Neurons, also be known as brain cells or nerve cells, work by sending information through electrical impulses within the cell and by sending chemical signals from one cell to another. The place where two neurons meet is called a synapse. A chemical known as a neurotransmitter is released by Neuron A where they then travel across a synapse and bind to receptors on Neuron B. This binding generates an electrical signal in Neuron B which transmits along the cell and to a synapse of another neighbouring neuron where a neurotransmitter is then released.
Figure 1 Neuron communication https://mhanational.org/neurons-how-brain-communicates
Over 100 different types of neurotransmitters, each with a unique role have been found within the human body. Abnormal levels of certain neurotransmitters can contribute to mental health conditions.
The two neurotransmitters which are commonly associated with depression are serotonin and noradrenaline (which is also known sometimes as norepinephrine).
Serotonin can stabilise mood, feelings of wellbeing, as well as regulate appetite, digestion and sleep. Low levels of serotonin can cause feelings of depression and anxiety.
Noradrenaline helps the body respond to stress and is elevated in response to fight or flight instincts. It also helps the body know when to wake up each morning, increases attention to tasks, and assists with memory storage. Too low levels of noradrenaline can be associated with depression, anxiety, PTSD and substance abuse, whereas too high levels can lead to euphoria and panic attacks.
Types of antidepressants
There are several different types of antidepressants, all of which work differently and have different risks and side effects.
Selective serotonin reuptake inhibitors (SSRIs)
SSRIs are the most widely prescribed type of antidepressants. SSRIs work by preventing serotonin from being reabsorbed from the neuron (brain cell) which originally released it. This encourages the serotonin to continue binding to the receiving neuron, meaning the neuron continues to transmit signals to reduce feelings of depression and anxiety. SSRIs are usually preferred over other antidepressants, as they cause fewer side effects. Fluoxetine (also known as Prozac) is the best known SSRI. Other SSRIs include citalopram (Cipramil), escitalopram (Cipralex), paroxetine (Seroxat) and sertraline (Lustral).
Serotonin-noradrenaline reuptake inhibitors (SNRIs)
SNRIs work in a similar way to SSRIs but they work on noradrenaline as well as serotonin. Examples of SNRIs include duloxetine (Cymbalta and Yentreve) and venlafaxine (Efexor).
Noradrenaline and specific serotonergic antidepressants (NaSSAs)
NASSAs may be effective for some people who are unable to take SSRIs. NaSSAs work by increasing the amount of noradrenaline and serotonin in the synapse and by also binding to serotonin receptors. The main NASSA prescribed in the UK is mirtazapine (Zispin).
Serotonin antagonists and reuptake inhibitors (SARIs)
SARIs are not usually the first choice of antidepressant, but they may be prescribed as an alternative to other antidepressants. SARIs work in a similar manner to SSRIs with the additional benefit of also redirecting serotonin to the specific parts of the brain which regulate mood. The main SARI prescribed in the UK is trazodone (Molipaxin).
Monoamine oxidase inhibitors (MAOIs)
MAOIs are rarely used nowadays a they can cause potentially serious side effects and risk interacting with other medications and certain foods. MAOIs target the monoamine oxidase enzyme in the brain which breaks down neurotransmitters including serotonin. This can lead to stabilised moods and less anxiety. Examples of MAOIs include tranylcypromine, phenelzine and isocarboxazid.
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