All antidepressants cause side effects. The most common problems are sleepiness, a dry mouth, constipation, nausea and sexual problems. These drugs can be dangerous to children. Elderly people are more likely to have a fall if they take antidepressants. And if you take too much of an antidepressant, you may damage your heart.
Different drugs have different risks. Here we've summarised the side effects that people had in studies.
The table below shows the percentages of people who had particular side effects while taking imipramine. Imipramine is a tricyclic antidepressant.
Side effect Percentage of people taking imipramine
Dry mouth 74%
People taking a dummy treatment (a placebo) for comparison also had these side effects. But the people who took the drugs were more likely to get side effects than people who took the placebo. About a quarter of the people who took a placebo said their tablets made them drowsy.
Drowsiness may wear off a little after you've been taking the drug for a while. The other side effects probably won't, however.
Taking too much of a tricyclic antidepressant, such as imipramine, can seriously damage your heart. If you take too many tablets by mistake, call for help immediately. You may need urgent treatment in hospital.
Imipramine is particularly dangerous for children. Children who accidentally swallow these tablets have a 1 in 44 risk of dying from poisoning. Keep all medicines in a locked cabinet, out of the reach of children.
If you're over 80, you're more likely to have a fall if you take imipramine.
Of the people who took venlafaxine in studies:
- About two-thirds had sexual problems, such as erection problems or difficulty having an orgasm
- About half felt sick
- About a third had trouble sleeping
- Just under a third had a dry mouth
- About a quarter felt tired
- About a quarter felt dizzy
- About 1 in 10 didn't feel like eating.
Venlafaxine's side effects are usually mild. They often get milder or disappear after the first couple of weeks of treatment. Unfortunately, the problems with sex don't improve with time. About 1 in 7 people stop taking venlafaxine because of side effects.
About 4 in 10 people taking an antidepressant called paroxetine (Seroxat) said the drug made them feel sick. In one survey, more than two-thirds of people said it affected how much they enjoyed having sex. 
Paroxetine is one of a group of antidepressants called selective serotonin reuptake inhibitors (or SSRIs for short). If you're over 65, SSRIs may lower the amount of salt in your blood. Very low levels of salt may cause seizures. Your doctor may recommend that you take another type of antidepressant. If you take paroxetine, your doctor may check the level of salt in your blood for a few weeks. 
If you're over 80, taking an SSRI may increase your risk of falling.
If you take too many tablets, SSRIs are not as bad for you as tricyclic antidepressants (such as imipramine). But you should still get medical help if you think you've taken too many.
What if I'm pregnant?
There isn't much research on taking antidepressants if you're pregnant. Doctors are advised to avoid prescribing them to pregnant women, or to use them with care if the benefits are likely to outweigh the risks. This is because of concerns that drugs taken during pregnancy might harm the baby.
- If you take antidepressants late in your pregnancy, your baby may get withdrawal symptoms soon after birth.
- In one study, some mothers who took fluoxetine late in their pregnancy had smaller babies.
One study looked at over 3,500 women who took antidepressants during the first three months of pregnancy. It found that women who took paroxetine (Seroxat) were more likely to have a baby with birth defects than women who took other antidepressants. The babies affected mainly had heart defects.
Earlier studies haven't shown a higher risk of birth defects from paroxetine or other selective serotonin reuptake inhibitors (SSRIs).
If you're pregnant or hope to get pregnant, discuss your options with your doctor. You may prefer to try a psychological treatment, such as cognitive behaviour therapy.
Can I get addicted to antidepressants?
Researchers don't think you can get addicted to antidepressants. But they disagree about how hard it is to stop taking them. In one study, 60 percent of people taking paroxetine had withdrawal symptoms when they stopped taking it.
In the UK, the government's Committee on Safety of Medicines (CSM) says:
- All SSRIs may cause withdrawal symptoms on stopping or reducing treatment
- Paroxetine and venlafaxine seem to cause withdrawal symptoms more often than other SSRIs
- Some withdrawal symptoms are severe
- The most common withdrawal symptoms are dizziness, numbness and tingling, stomach upset (particularly nausea and vomiting), headache, sweating, anxiety and sleep disturbances
- Doctors and patients need to be more aware of the risk of withdrawal symptoms associated with SSRIs. You might get fewer of these symptoms if you reduce the dose of SSRI you take gradually over a period of several weeks. Your doctor will advise you how to do this.
Talk to your doctor if you want to stop taking an antidepressant. And never stop your treatment suddenly.
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A placebo is a 'pretend' or dummy treatment that contains no active substances. A placebo is often given to half the people taking part in medical research trials, for comparison with the 'real' treatment. It is made to look and taste identical to the drug treatment being tested, so that people in the studies do not know if they are getting the placebo or the 'real' treatment. Researchers often talk about the 'placebo effect'. This is where patients feel better after having a placebo treatment because they expect to feel better. Tests may indicate that they actually are better. In the same way, people can also get side effects after having a placebo treatment. Drug treatments can also have a 'placebo effect'. This is why, to get a true picture of how well a drug works, it is important to compare it against a placebo treatment.
Withdrawal symptoms are when you get unpleasant physical or mental symptoms because you stopped taking a drug you were physically dependent on. Your can become physically dependent on a drug if it alters the level of certain chemicals in your body. This makes your body produce less of those chemicals or change how it responds to them. Also, some drugs work in a similar way to chemicals that naturally occur in your body. This may mean your body stops making its natural versions. If either of those things happens, your body will need the drug to function normally and you will feel or become ill if you suddenly stop taking the drug. You can get withdrawal symptoms from some prescription medicines, as well as some illegal drugs.
A seizure (or fit) is when there is too much electrical activity in your brain, which results in muscle twitching and other symptoms.
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