Drugs that are used to treat the symptoms of depression
Antidepressant drugs help to relieve many symptoms of depression, such as despair, lethargy, poor appetite, insomnia, and thoughts of suicide. Some types of antidepressants, such as selective serotonin reuptake inhibitors (SSRIs), are also effective in treating certain other psychological problems, such as anxiety and post-traumatic stress.
People who are depressed have been shown to have reduced levels of certain chemicals called neurotransmitters in the brain. Serotonin and norepinephrine (noradrenaline) are two neurotransmitters that are thought to increase brain activity and improve mood. They are usually reabsorbed by brain cells and inactivated by an enzyme called monoamine oxidase. In a depressed person, levels of serotonin or norepinephrine are frequently lower than normal. Anti-depressants work by helping to restore these chemicals to normal levels.
Antidepressants are taken orally and usually take 2–3 weeks to have an effect on depression. Side effects may develop immediately but gradually lessen. Your doctor will usually advise you to take an antidepressant for at least 4–6 months after your depression has lifted to prevent symptoms recurring and then to reduce the dose gradually. You should avoid alcohol while you are taking these drugs because it enhances the sedative effect.
Most of the drugs used to treat depression belong to one of three main groups: selective serotonin reuptake inhibitors (SSRIs), tricyclics, and monoamine oxidase inhibitors (MAOIs). There are also several other types of antidepressant. All of these drugs treat depression by increasing levels of the neurotransmitters in the brain that lift mood.
These drugs are the most commonly used type of antidepressant. They may also be used to treat anxiety disorders and post-traumatic stress disorder. SSRIs cause fewer side effects than other types of antidepressant and are less toxic if more than the prescribed amount is taken. The drugs work by blocking the reabsorption of the neurotransmitter serotonin, leaving more of the chemical to stimulate brain cells (see How SSRIs work). SSRIs may cause side effects, including diarrhoea, nausea and vomiting, reduced sex drive, and headache. They may also cause restlessness and anxiety. Most SSRIs are not recommended for treating depression in those under 18 years old.
Tricyclics are often used to treat depression. They interfere with the reabsorption of serotonin and norepinephrine in the brain; as a result, levels of these mood-lifting chemicals increase. They are also sometimes used to treat pain from damaged nerves in conditions such as trigeminal neuralgia.
Tricyclics cause a number of side effects, including a dry mouth, blurred vision, constipation, and difficulty in passing urine. The side effects are usually worse when the drug is first started and become less of a problem as you get used to the drug. Tricyclics are dangerous if you exceed the usual dose. They may cause seizures and heart rhythm irregularities, which can be fatal.
These drugs are usually only used when other types of antidepressant drug are ineffective. They work by blocking the activity of monoamine oxidase (the enzyme that makes serotonin and norepinephrine inactive) in brain cells. The side effects may include light-headedness, drowsiness, insomnia, headache, a dry mouth, constipation, and other digestive problems. MAOIs interact with a wide range of other drugs and with food and drink containing tyramine (for example, cheese, meat and yeast extracts, pickled herring, fermented soya bean extract, red wine, and some other alcoholic and low-alcohol drinks). These interactions can cause a dangerous rise in blood pressure and it is therefore important that you follow your doctor’s instructions about taking MAOIs and consult your doctor or pharmacist before taking any over-the-counter medications or complementary remedies. When planning to stop taking an MAOI, the dose should be reduced gradually to minimize the risk of dangerous changes in blood pressure.
Mianserin and trazodone are related to tricyclic antidepressants. They are used to treat depression when sedation is required. Trazodone is less likely to cause heart rhythm problems than other tricyclics. Mirtazepine increases serotonin and norepinephrine levels in the brain. It initially causes sedation and may sometimes cause potentially serious blood disorders. Flupentixol may cause restlessness and agitation and is therefore not suitable for people who are easily excitable and overactive. Reboxetine inhibits the reuptake of norepinephrine in the brain, and venlafaxine inhibits the reuptake in the brain of both serotonin and norepinephrine. Venlafaxine tends to produce fewer side effects than many antidepressants, but you should consult your doctor if you develop a rash while taking it.
Antidepressant drugs can cause drowsiness and may affect your ability to drive vehicles or operate machinery.
From the 2010 revision of the Complete Home Medical Guide © Dorling Kindersley Limited.