Do Antidepressants Lower IQ? What the Research Shows

Antidepressants do not lower IQ: in randomised trials of people with depression they produce small improvements in memory and processing speed, roughly 2 to 4 IQ-point equivalents, and in healthy volunteers they show no measurable effect on thinking in either direction. The mental slowness many people notice during treatment is real, but the research points mostly to depression itself, which lowers scores on memory, attention and planning tasks by about 5 to 10 IQ-point equivalents and often lingers after mood improves.

This page covers how depression affects test performance, what controlled trials show about antidepressants, why some people feel duller on medication, and what is known about antidepressants in pregnancy and children's IQ. It describes research findings and is not medical advice. Decisions about starting, changing or stopping an antidepressant belong with your prescriber.

Any honest answer has to start with the illness, because most people who take antidepressants take them for depression, and depression itself affects thinking. In a meta-analysis of studies that all used the same computerised test battery, Rock and colleagues found that people with depression scored below healthy controls on executive function, memory and attention, with effect sizes (Cohen's d) from -0.34 to -0.65. Because the IQ scale has a "standard deviation" (the typical spread of scores around the average) of 15 points, those gaps work out to roughly 5 to 10 IQ-point equivalents on specific tasks. These are gaps on specific tasks, which is a narrower thing than a drop in full-scale IQ.

The deficits do not simply vanish when mood lifts. In the same meta-analysis, people whose depression had remitted still showed moderate deficits in executive function and attention (d from -0.52 to -0.61). A three-year study of 267 primary care patients by Conradi and colleagues found that cognitive problems were one of the most persistent symptoms. Together with low energy and poor sleep, they were present 85 to 94% of the time during depressive episodes and 39 to 44% of the time during remission.

This is the main reason the question is hard to study. If you compare people taking antidepressants with people who are not, the users are, on average, people who have been depressed, and depression alone predicts lower scores. Researchers call this "confounding by indication." The reverse question, whether IQ affects the risk of becoming depressed, is covered in our article on the link between IQ score and depression.

Randomised trials avoid that problem by assigning treatment by chance.

• The 2016 meta-analysis of placebo-controlled trials: Joshua Rosenblat, Ron Kakar and Roger McIntyre pooled nine trials with 2,550 people with major depression. Antidepressants improved delayed recall (a standardised mean difference of 0.24) and psychomotor speed (0.16), and had no significant effect on executive function. On the IQ metric those effects are about 3.6 and 2.4 points, and the speed effect lost significance once vortioxetine trials were removed. Head-to-head trials found no difference in cognitive effects between the main drug classes.

• The 2018 meta-analysis across samples: Catherine Prado, Stephanie Watt and Simon Crowe analysed 33 studies. In depressed participants, antidepressants had modest positive effects on attention, executive function, memory and processing speed, with SSRIs (selective serotonin reuptake inhibitors, the most widely prescribed class) showing the largest benefit. In non-depressed participants, antidepressants did not significantly affect cognition.

• The iSPOT-D trial: Carrie Shilyansky and colleagues randomly assigned 1,008 medication-free adults with depression to escitalopram, sertraline or extended-release venlafaxine and retested them after eight weeks. Impairments in five areas, including attention, verbal memory and information processing, did not improve relative to healthy controls, even in patients whose depression remitted, and the three drugs did not differ. The medication eased mood without repairing the cognitive side of depression.

Taken together, these trials point in one direction. Antidepressants are associated with small cognitive gains in depression, probably because they ease the illness, and they leave some of the cognitive burden of depression untouched. None of these trials or meta-analyses found that they lower measured ability.

The cleanest test of a direct drug effect is to give an antidepressant to people who are not depressed. In a randomised trial by Ulla Knorr and colleagues, 80 healthy first-degree relatives of people with depression took escitalopram or a placebo for four weeks. A general cognition score built from 13 test measures did not change with the drug, and no single test did either. The authors concluded that escitalopram neither improved nor impaired cognition, and that the gains seen in depressed patients probably reflect relief of depressive symptoms.

Prado's meta-analysis reached the same conclusion for non-depressed samples generally. So the evidence answers both popular versions of the question: antidepressants do not make healthy people smarter, and they do not make them less intelligent.

Many people on long-term treatment report thinking problems. Maurizio Fava and colleagues surveyed 117 people whose depression had responded to antidepressants and found that apathy, inattentiveness, forgetfulness, word-finding difficulty and mental slowing were each reported by more than 30%. The authors judged that these complaints probably reflect both side effects of the drugs and leftover symptoms of depression.

The type of drug matters too. Some antidepressants, including several older tricyclics, have strong "anticholinergic" effects (they block acetylcholine, a chemical messenger involved in memory). In an English primary care study of 58,769 people with dementia and 225,574 controls aged 55 or older, Carol Coupland and colleagues found that more than 1,095 standard daily doses (about three years' worth) of strongly anticholinergic antidepressants was associated with 29% higher odds of dementia. That study is observational and cannot fully separate the drug from the reasons it was prescribed, and it concerns only antidepressants classed as strongly anticholinergic, not the drug class as a whole.

If you notice memory or concentration changes on a medication, the person to talk to is your prescriber, a GP or a pharmacist, who can check whether the drug, the dose, the timing or the depression itself is the more likely cause. Anxiety can produce similar complaints, as our article on anxiety and IQ explains.

A separate worry is whether exposure before birth affects a child's later intelligence. This is where confounding by indication matters most, because mothers who need antidepressants differ from mothers who do not.

• The Toronto cohort: Irena Nulman and colleagues found that children exposed to venlafaxine or SSRIs in pregnancy had full-scale IQs of 105, similar to children of mothers with untreated depression (108). Both were below children of healthy mothers (112), and the mother's own IQ was a key predictor of the child's.

• The Toronto sibling study: comparing 45 pairs of siblings where only one was exposed, the same group found no significant difference in full-scale IQ (103 vs 106), and dose and duration did not predict outcomes.

• The Danish school-test study: Jakob Christensen and colleagues followed 575,369 schoolchildren. Exposed children scored 2.2 points lower in mathematics on a 1-to-100 scale (2.8 points within sibling pairs) and showed no difference in language. The authors called the gap small and of uncertain clinical importance, to be weighed against the benefits of treating depression in pregnancy.

• The US insurance cohorts: in 3.18 million pregnancies, Elizabeth Suarez and colleagues found that crude analyses suggested up to a doubling in risk of neurodevelopmental disorders, but comparisons of exposed and unexposed siblings found no association, including a hazard ratio of 1.00 for intellectual disability.

The pattern is the usual one for confounding: large crude differences that shrink or disappear once family background is held constant. Anyone pregnant or planning a pregnancy who takes an antidepressant should discuss it with their prescriber or obstetrician.

The trial evidence says no. In depressed patients they are linked to small improvements in memory and speed, and in healthy volunteers they show no measurable effect on cognition.

Not in a lasting sense. The small gains seen in depression are probably the result of easing the illness, and in non-depressed people antidepressants did not significantly change test performance.

Cognitive complaints are common during treatment and can come from side effects such as drowsiness, from leftover depressive symptoms, or from both. Your prescriber is the right person to help work out which.

It lowers performance on memory, attention and executive function tasks by roughly 5 to 10 IQ-point equivalents, and some of the deficit persists after mood improves. Testing during a depressive episode can underestimate ability.

Sibling comparisons find little or no difference, which suggests that most of the gaps in simpler comparisons reflect the mother's depression and family background. This is a decision to make with a prescriber or obstetrician.

The fear that antidepressants erode intelligence is not supported by controlled research. Depression itself lowers cognitive test performance, antidepressants are linked to small improvements during treatment, and healthy volunteers show no change. The fog some people describe is real and worth raising with a prescriber, but it is better explained by side effects and lingering symptoms than by lost ability. If you want an accurate reading of your reasoning ability, choose a time when you feel well and take a full-length online IQ test.

1. Rock, P. L., Roiser, J. P., Riedel, W. J., & Blackwell, A. D. (2014). Cognitive impairment in depression: A systematic review and meta-analysis. Psychological Medicine, 44(10), 2029-2040. [doi.org/10.1017/S0033291713002535](. doi.org

2. Conradi, H. J., Ormel, J., & de Jonge, P. (2011). Presence of individual (residual) symptoms during depressive episodes and periods of remission: A 3-year prospective study. Psychological Medicine, 41(6), 1165-1174. [doi.org/10.1017/S0033291710001911](. doi.org

3. Rosenblat, J. D., Kakar, R., & McIntyre, R. S. (2016). The cognitive effects of antidepressants in major depressive disorder: A systematic review and meta-analysis of randomized clinical trials. International Journal of Neuropsychopharmacology, 19(2), pyv082. [doi.org/10.1093/ijnp/pyv082](. doi.org

4. Prado, C. E., Watt, S., & Crowe, S. F. (2018). A meta-analysis of the effects of antidepressants on cognitive functioning in depressed and non-depressed samples. Neuropsychology Review, 28(1), 32-72. [doi.org/10.1007/s11065-018-9369-5](. doi.org

5. Shilyansky, C., Williams, L. M., Gyurak, A., Harris, A., Usherwood, T., & Etkin, A. (2016). Effect of antidepressant treatment on cognitive impairments associated with depression: A randomised longitudinal study. The Lancet Psychiatry, 3(5), 425-435. [doi.org/10.1016/S2215-0366(16)00012-2](. doi.org

6. Knorr, U., Vinberg, M., Gade, A., Winkel, P., Gluud, C., Wetterslev, J., Gether, U., & Kessing, L. (2011). A randomized trial of the effect of escitalopram versus placebo on cognitive function in healthy first-degree relatives of patients with depression. Therapeutic Advances in Psychopharmacology, 1(5), 133-144. [doi.org/10.1177/2045125311422591](. doi.org

7. Fava, M., Graves, L. M., Benazzi, F., Scalia, M. J., Iosifescu, D. V., Alpert, J. E., & Papakostas, G. I. (2006). A cross-sectional study of the prevalence of cognitive and physical symptoms during long-term antidepressant treatment. Journal of Clinical Psychiatry, 67(11), 1754-1759. [doi.org/10.4088/jcp.v67n1113](. doi.org

8. Coupland, C. A. C., Hill, T., Dening, T., Morriss, R., Moore, M., & Hippisley-Cox, J. (2019). Anticholinergic drug exposure and the risk of dementia: A nested case-control study. JAMA Internal Medicine, 179(8), 1084-1093. [doi.org/10.1001/jamainternmed.2019.0677](. doi.org

9. Nulman, I., Koren, G., Rovet, J., Barrera, M., Pulver, A., Streiner, D., & Feldman, B. (2012). Neurodevelopment of children following prenatal exposure to venlafaxine, selective serotonin reuptake inhibitors, or untreated maternal depression. American Journal of Psychiatry, 169(11), 1165-1174. [doi.org/10.1176/appi.ajp.2012.11111721](. doi.org

10. Nulman, I., Koren, G., Rovet, J., Barrera, M., Streiner, D. L., & Feldman, B. M. (2015). Neurodevelopment of children prenatally exposed to selective reuptake inhibitor antidepressants: Toronto sibling study. Journal of Clinical Psychiatry, 76(7), e842-e847. [doi.org/10.4088/JCP.14m09240](. doi.org

11. Christensen, J., Trabjerg, B. B., Sun, Y., & Dreier, J. W. (2021). Association of maternal antidepressant prescription during pregnancy with standardized test scores of Danish school-aged children. JAMA, 326(17), 1725-1735. [doi.org/10.1001/jama.2021.17380](. doi.org

12. Suarez, E. A., Bateman, B. T., Hernández-Díaz, S., Straub, L., Wisner, K. L., Gray, K. J., Pennell, P. B., Lester, B., McDougle, C. J., Zhu, Y., Mogun, H., & Huybrechts, K. F. (2022). Association of antidepressant use during pregnancy with risk of neurodevelopmental disorders in children. JAMA Internal Medicine, 182(11), 1149-1160. [doi.org/10.1001/jamainternmed.2022.4268](. doi.org

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