What are antidepressants?

Antidepressants are drugs prescribed by doctors to treat depression, anxiety, post-traumatic stress disorder and/or obsessive compulsive disorder as well as some other conditions. Antidepressants appear to work by increasing the amounts of certain chemicals (neurotransmitters) such as serotonin and noradrenaline in the brain. These chemicals are thought to be responsible for regulating mood.

The jury is still out on how well antidepressants work. The Royal College of Psychiatrists suggest that around 50-65% of people taking antidepressants see some benefit, compared to 25-30% who took a placebo. They seem to be most effective at helping more severe types of depression. Antidepressants can also have unwanted side effects such as nausea, feeling anxious, diarrhoea, constipation and a lower sex drive.


Prozac (Fluoxetine)

There are several types:

SSRIs (Serotonin Re-uptake Inhibitors) work by blocking the reabsorption of serotonin in the brain. SSRIs include Sertraline (Lustral) and Fluoxetine (Prozac) which is the most widely prescribed antidepressant in the world. These are thought to be the safest type of antidepressant.

SNRIs (Serotonin and Norepinephrine Re-uptake Inhibitors) work by affecting serotonin and norepinephrine levels in the brain. SNRIs include Venlafaxine/Effexor Some people respond better to SNRIs than SSRIs and vice versa.

NASSAs (Noradrenaline and specific serotonergic antidepressants)

NASSAs may be effective for some people who are unable to take SSRIs.

MAOIs (monoamine oxidase inhibitors) act by inhibiting the activity of monoamine oxidase, thus preventing the breakdown of monoamine neurotransmitters and thereby increasing their availability. This in turn increases the levels of ‘feel-good’ neurotransmitters such as serotonin, norepinephrine and dopamine, by preventing their breakdown in the brain. They are not prescribed very often any more.

Tricyclic antidepressants (TCAs) are an older type of antidepressant. They are no longer usually recommended as a first-line treatment for depression because they can be more dangerous in overdose. TCAs include amitriptyline (Elavil), desipramine (Norpramin), imipramine (Tofranil), nortriptyline (Pamelor), protriptyline (Vivactil) and trimipramine (Surmontil).

Most antidepressants take a few weeks to start working.


There has been alarm over the large number of prescriptions being written for antidepressants. According to NHSBSA’s Medicines Used in Mental Health – England – 2015/16 to 2020/21 statistics, there were 79.4 million antidepressant drug items prescribed to 7.87 million patients in 2020/21. The number of antidepressant items issued and the number of patients receiving antidepressant drugs increased for the fifth consecutive year. 

Street use

Antidepressants are not generally used as street drugs however there has been some evidence of Prozac use in combination with drugs such as LSD, ecstasy or cannabis.

Addictive potential

People do not develop a tolerance to antidepressants in the same way as they do to alcohol or opiates, which require increasing dosages to maintain their effect. However, studies have shown that people may become psychologically dependent, and that about one third of patients experience withdrawal symptoms when they stop taking these drugs.

Withdrawal symptoms include increased anxiety, dizziness, flu like symptoms, stomach aches and nightmares. It is best to talk to your doctor about coming off antidepressants and to do so gradually.

Interactions with other drugs

Antidepressants may interact with street drugs in ways that can cause problems.

Cannabis has been found to interact with certain types of antidepressants, such as tricyclic antidepressants (TCAs), which share similar side effects.

It is best to avoid alcohol while taking antidepressants because alcohol can make depression worse. It can also increase the side effects of some antidepressants, such as drowsiness, dizziness and coordination problems.

Always read the information leaflet that comes with your drugs and/or talk to your doctor.

The law

Antidepressants are Prescription Only drugs. They are controlled under the Medicines Act but not under the Misuse of Drugs Act. It is not an offence to be in possession of antidepressants without a prescription but it is an offence to supply it (including giving it away free) to other people.

See also:

Blog: The depressing truth about antidepressants

Prescribed medicines review: report, 2019
Report of the review of the evidence for dependence on, and withdrawal from, prescribed medicines | PHE, UK

Updated March 2022