Can You Lower Your IQ? Why Scores Drop—and When It Means Something

A lower IQ score can tell two very different stories: you performed worse on that test, or the abilities behind the score actually changed. Those explanations should never be treated as interchangeable.

Yes, an IQ score can go down, and underlying cognitive ability can also decline in some circumstances. A single lower result, though, does not prove that you permanently became less intelligent. Sleep, test familiarity, normal measurement variation, development, neurological injury, and other factors can produce very different kinds of change.

If you need the foundation first, our guide to what an IQ score actually means explains how IQ compares your performance with people in your age group. You can also explore the broader subject in Cognitive Train’s Intelligence & IQ guides.

First, Separate a Lower Score From Lower Intelligence

An IQ test is a measurement taken under a particular set of conditions. It is not a permanent number stamped onto your brain.

One clear demonstration comes from retesting. In a WAIS-IV study of 54 participants, Full Scale IQ rose by about seven points on average when the same people were tested again three or six months later. The researchers concluded that the gains reflected practice effects from previous exposure to the test, not genuine intellectual growth.

That matters in both directions. If familiarity can push a score upward, a less familiar test, a different format, or poorer test-day performance can make comparisons messy. A change in the number is evidence that test performance changed. You still have to ask why.

This is especially important with online tests, where formats and scoring systems vary widely. Cognitive Train’s guide to online IQ test accuracy explains why two sites can give the same person different-looking results.

Sleep Can Make You Perform Worse Without Proving Your IQ Fell

Sleep is a good example of why the distinction matters.

A meta-analysis covering 61 studies found that short-term sleep restriction produced an overall decline in cognitive performance, including significant effects on executive function, sustained attention, and long-term memory. The same review found insufficient evidence to establish an effect specifically within intelligence measures.

So “I tested lower after sleeping badly” and “sleep permanently lowered my intelligence” are very different claims. Poor sleep can make attention, memory, and mental control less reliable on the day you are tested. That can drag down performance without demonstrating lasting loss of intellectual capacity.

Our guide to what sleep does to the thinking brain covers those temporary performance effects in more detail.

IQ Can Genuinely Move During Development

IQ is fairly stable compared with many psychological measures, but stable does not mean frozen.

A longitudinal neuroimaging study of teenagers found that verbal and nonverbal IQ scores could rise or fall over the teenage years. The changes were associated with changes in local brain structure, giving the researchers reason to treat them as more than random test noise.

Because IQ is age-normed, a falling score can also mean that your performance improved more slowly than that of your age peers. You do not necessarily have to lose an absolute skill for your relative standing to change.

Cognitive Train’s article on how IQ changes with age follows this across childhood, adulthood, and later life. For the longer-term question, see how stable IQ scores are over time.

Serious Brain Injury Can Produce Lasting Declines

There are also situations where a lower cognitive score can reflect genuine neurological change.

A meta-analysis of 81 studies involving 3,890 patients examined intelligence after traumatic brain injury. In the chronic phase, Full Scale IQ impairment was small on average after mild or moderate TBI and remained large after severe TBI. The authors concluded that TBI can produce persistent impairments in measured intelligence, with injury severity strongly related to outcome.

This is one reason a major, unexpected change in thinking after an injury should not be interpreted through repeated online testing alone. Formal neuropsychological assessment looks at the pattern of abilities and the medical context, not a single number.

Developmental Toxic Exposure Can Affect IQ Too

Some environmental exposures can interfere with brain development.

One influential pooled analysis combined seven longitudinal cohorts totaling 1,333 children. Higher blood lead concentrations were associated with lower Full Scale IQ scores across the childhood exposure range studied. Lead is a neurotoxin, and childhood exposure is a very different situation from an adult having a rough week or performing badly on one test.

The useful takeaway is that genuine losses in cognitive development are possible under harmful biological conditions. That does not mean ordinary day-to-day mistakes or a temporary slump have “damaged your IQ.”

Does Aging Automatically Lower Your IQ?

No. Aging changes the profile of cognitive abilities more than it produces one simple downward line.

Processing speed and some forms of novel problem solving often become harder with age, while accumulated knowledge can remain strong for much longer. Because IQ batteries combine different abilities and compare people with age peers, the final score can hide meaningful changes inside the profile.

That is why a lower processing-speed score is not automatically the same as lower general intelligence. Our guide to processing speed and IQ explains that relationship.

If Your IQ Score Dropped, Ask These Questions First

Before deciding that you became less intelligent, look at the comparison itself. Was it the same test? Were the scoring norms comparable? Had you seen one version before? Were you well rested? Did one result come from a quick online quiz and the other from a longer standardized assessment?

Then look for consistency. A one-off lower score means much less than a repeated pattern across several abilities and settings.

If you have noticed a significant new decline in everyday thinking—especially after an injury or alongside other neurological symptoms—a professional assessment is more informative than repeatedly taking online IQ tests.

Use an IQ Estimate as a Baseline, Not a Verdict

Cognitive Train’s IQ-Style Test samples several reasoning-related abilities and gives an approximate estimate with a skill breakdown. It can be useful as a baseline when you take it under ordinary, rested conditions.

Avoid retesting immediately just to chase a different number. Familiarity itself can change performance, which makes the comparison harder to interpret.

For more targeted measures, explore Cognitive Train’s brain tests and cognitive assessments.

So, Can You Lower Your IQ?

Yes, IQ scores can fall, and real cognitive ability can decline in some circumstances. The important part is figuring out which kind of change you are looking at.

A bad night, unfamiliar test, or noisy score is not the same thing as persistent cognitive decline. Development can shift IQ relative to peers, and serious neurological injury or harmful developmental exposure can produce more lasting changes. The number only becomes meaningful once you understand the reason it moved.

If you are interested in the other direction, see whether IQ can increase. You can also browse Cognitive Train’s brain training and cognitive training tools for ways to practice specific abilities such as reasoning, memory, attention, and processing speed.