Selective Serotonin Re-uptake Inhibitors

SSRIs, Selective Serotonin Re-uptake Inhibitors, are a widely used group of antidepressants, which includes such drugs as fluoxetine (Prozac) and paroxetine (Seroxat).


SSRIs are mostly used for treatment of depression, but individual members of the group have other, specialized uses for example for anxiety, panic disorder, obsessive compulsive disorder, eating disorders, and social phobia.

SSRIs only work after they have built up in your system, and thus need to be taken regularly, and will start to have their effects after two weeks or more.

How they work

The brain is made up of millions of interconnected brain cells (neurons). Messages travel along these cells rather like electricity down a wire, but when the message reaches the end of the neuron, it has to jump the gap (synapse) to the next cell or group of cells.

This is achieved by the neuron releasing tiny amounts of a chemical (neurotransmitter) into the gap between the nerve cells.

The receiving neuron has many places on its surface which act rather like locks, for which the appropriate neurotransmitter is the key. These are called receptors. When enough of the neurotransmitter has locked on to these receptors, a nerve impulse is started in the new nerve, and thus the message gets from one nerve to the next.

In order to allow the nerve to recover and receive the next message, and in order to replenish stocks of the neurotransmitter in the original neuron, ready to send the next message, the body has a clever way of removing the neurotransmitter from the receptors, and allowing it to be taken back into the originating nerve (re-uptake).

In depression certain neurotransmitters are relatively lacking. One of those is serotonin, also known as 5-hydroxytryptamine or 5-HT. The SSRIs (Selective Serotonin Re-uptake Inhibitors) slow down the process of returning the serotonin to the end of the neuron it comes from. This leads to the chemical remaining in the vicinity of the receptors for longer, making it more likely that enough will build up to set off the impulse in the next neuron.

Thus, the SSRIs work by allowing the body to make the best use of the reduced amounts of serotonin that it has at the time. In due course, the levels of natural serotonin will rise again, and the SSRI can be reduced and withdrawn.

Adverse reactions

Remember to tell the doctor if you are allergic to anything.

Always read the advice leaflets that come with your medication, and follow the instructions on the bottle or box.

If you develop any symptoms that you think may be side effects, discuss them with your doctor. If they are serious or troublesome, stop taking the medication and discuss with your doctor when you are able to.

The most common side effects are gastrointestinal, that is feeling sick, vomiting, indigestion, abdominal pain, diarrhea or constipation. Other side effects include:

  • loss of appetite, weight loss
  • increased appetite, weight gain
  • allergic reactions
  • dry mouth
  • irritability / anxiety
  • sleeplessness
  • drowsiness
  • headache
  • shaking
  • dizziness
  • fits / convulsions
  • disturbance of sexual function (but this is also a feature of depression)
  • sweating
  • bruising
  • manic or hypomanic behavior
  • abnormal movements
  • low sodium level
  • suicidal ideas

As you will see, just about everything has been reported in people taking these drugs. Most of these are unlikely to happen. If you do get side effects, the most likely is nausea, and most often this is only bad for a few days. The good effects, however may take 2-6 weeks to come on, so it pays to be patient if you can.


  • The doctor will be cautious about using them in someone with epilepsy,
  • Best not used in poorly controlled epilepsy.
  • The UK MHRA advises against use of these drugs to treat major depressive disorder (MDD) in those under 18 years of age, except for fluoxetine (Prozac).
  • Caution in someone who is receiving Electro Convulsive Therapy (ECT).
  • Caution in people with a history of manic illness, heart disease, liver or kidney disease, or bleeding disorders.
  • As always, caution should be used in pregnancy or breast feeding.
  • SSRIs may impair performance of tasks requiring skill and coordination.
  • SSRIs are best not stopped suddenly. Discuss stopping them with your doctor. (This is usually after 3-6 months.)

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