Medications That Can Cause Brain Fog, and How to Tell

Yes, medication can cause brain fog. The usual culprits are medicines that sedate the brain or block a chemical messenger called acetylcholine: some sleep aids and allergy pills, benzodiazepines, and certain antidepressants, antipsychotics and seizure medicines. Effects are more likely when a medicine is new, its dose has gone up, or several sedating drugs are combined, and older adults are more sensitive. The clue is usually timing. This guide explains which medicines to look at, how to tell a medication cause from other causes, and why the answer is a plan with your prescriber, not stopping on your own.

How a medicine can cloud thinking

Most medication-related fog comes from a few mechanisms:

• Sedation. Drugs that calm the central nervous system slow reaction time and make it harder to stay alert. Effects add up when two or more are taken together, including alcohol.
• Anticholinergic action. Acetylcholine supports memory and attention. Drugs that block it can cause confusion and forgetfulness along with dry mouth and constipation.
• Hangover effects. A bedtime medicine may still be active the next morning.
• Disrupted sleep. Some medicines fragment sleep or cause vivid dreams, and poor sleep then dulls thinking.

Anticholinergic medicines: small effects that add up

The American Geriatrics Society’s 2023 Beers Criteria list medications with strong anticholinergic properties. The list crosses many specialties, which is why nobody notices the total:

• First-generation antihistamines such as diphenhydramine, doxylamine and hydroxyzine, found in many nighttime cold, allergy and “PM” pain products. The Beers panel notes they are highly anticholinergic and that tolerance develops when they are used for sleep.
• Bladder medicines for overactive bladder, such as oxybutynin and related drugs.
• Some antidepressants: older tricyclics (for example amitriptyline, imipramine and nortriptyline) and paroxetine.
• Some antipsychotics, including chlorpromazine, clozapine and olanzapine.
• Certain stomach antispasmodics, muscle relaxants and nausea medicines.

For adults 65 and older, the criteria advise avoiding more than one anticholinergic medicine at a time because the combination raises the risk of cognitive decline. Longer-term questions remain: a study of 3,434 adults aged 65 and over in Seattle linked higher cumulative use of strong anticholinergics with a higher rate of later dementia. Because it was observational, it cannot show the drugs caused it. For a full regimen check, see our guide to a psychiatric medication review.

Benzodiazepines and sleep medicines

Benzodiazepines are prescribed for anxiety, panic, sleep and seizures. The Beers Criteria state that, in older adults, all benzodiazepines increase the risk of cognitive impairment, delirium, falls, fractures and motor vehicle crashes. The criteria were written for adults 65 and older; younger people vary in how strongly they notice sedation, which is why the timeline of your own symptoms matters.

“Z-drug” sleep medicines (eszopiclone, zaleplon and zolpidem) have adverse effects similar to benzodiazepines in older adults, according to the same criteria, with only small improvements in sleep. The zolpidem label warns that next-day impairment, including impaired driving, is more likely when it is taken with less than a full night (7 to 8 hours) of sleep remaining or with other central-nervous-system depressants.

The fix is not to stop. In 2020 the FDA required a boxed warning on all benzodiazepines about abuse, dependence and withdrawal reactions, and stopping suddenly after regular use can be dangerous. Our benzodiazepine tapering guide explains how a supervised reduction works, and why sleep medication may not be fixing your insomnia covers alternatives.

Antidepressants, antipsychotics and seizure medicines

Antidepressants

Sedating antidepressants and strongly anticholinergic ones are the most likely to affect thinking. Some people also describe feeling emotionally flat on an SSRI or SNRI, which can feel like fog but is a different problem; see emotional blunting on antidepressants. Untreated depression itself impairs concentration, so a fog that predates the medicine points elsewhere. Read how depression affects thinking.

Antipsychotics

Several antipsychotics are sedating, and a few are strongly anticholinergic. The quetiapine label, for example, carries a warning that the drug has the “potential to impair judgment, thinking, or motor skills,” with sleepiness most common early in treatment.

Seizure and mood-stabilizing medicines

Some anticonvulsants, which are also used for mood, migraine and pain, affect cognition. The topiramate label lists cognitive-related dysfunction, including confusion, psychomotor slowing, trouble with attention and memory, and word-finding difficulty, and notes these were more frequent with a fast increase in dose. The label also warns that antiepileptic drugs should not be stopped abruptly.

Opioids, muscle relaxants and other central-nervous-system drugs belong in the same conversation. For older adults, the Beers panel advises against combining three or more central-nervous-system-active drugs because of the risk of falls and fractures. More detail on side effects in general is in common psychiatric medication side effects.

Quick reference: medication groups and thinking

This table is not a list of drugs to avoid. Each of these medicines can be the right choice for a particular person; the point is to know which ones to ask about.

How to tell whether it is the medication

A medication cause is more likely when several of these line up:

• The fog began, or clearly worsened, within days to weeks of starting a medicine, raising a dose or adding a second sedating drug.
• It follows the dosing schedule: worse an hour or two after a dose or the morning after a bedtime pill.
• Other side effects from the same group arrived at the same time, such as dry mouth, constipation or unsteadiness.
• An over-the-counter sleep or allergy product became a nightly habit.

Other causes need to be ruled out at the same time: poor sleep, depression, anxiety, thyroid problems, low B12 or iron, and other medical conditions. A brain fog evaluation looks at all of them together.

Measuring can help. If a planned change is coming, some clinicians record a cognitive baseline before it and repeat the same tasks afterward, along with symptom ratings. Creyos is one tool for this; our Creyos guide explains what it measures. Repeat scores are affected by practice, sleep and mood, so they support the conversation rather than settling it.

Why you should not stop on your own

Stopping a medicine suddenly can cause withdrawal, rebound anxiety or insomnia, a return of the original condition, or, with some drugs such as benzodiazepines and seizure medicines, seizures. It also removes the information you need: if you stop two things at once, you won’t know which one mattered. A safer path:

1. Write down when the fog started and what changed around then.
2. Bring every bottle, including supplements and over-the-counter products, to your prescriber.
3. Agree on one change at a time, with a planned taper if one is needed. Our guide to psychiatric medication tapering explains why slow matters.
4. Track thinking, sleep and mood before and after the change.

At Willow & Stone, Dr. Stacey Forbes, DNP, APRN, PMHNP-BC, can review your full medication list with you and plan any change together. Whether a Creyos baseline is part of that, and its cost, are confirmed when you book.

Common Questions

Sources & Further Reading

• American Geriatrics Society 2023 Updated AGS Beers Criteria (J Am Geriatr Soc, full text)
• Gray et al. 2015 — Cumulative use of strong anticholinergics and incident dementia (JAMA Intern Med)
• FDA — Boxed warning updated to improve safe use of benzodiazepine drug class (2020)
• DailyMed — Zolpidem (Ambien) prescribing information, §5.2 next-day impairment
• DailyMed — Quetiapine (Seroquel) prescribing information, potential for cognitive and motor impairment
• DailyMed — Topiramate (Topamax) prescribing information, §5.6 cognitive/neuropsychiatric adverse reactions

This article is general education, not a diagnosis or advice for your situation. Creyos results support, and never replace, a clinical evaluation; only a clinician who has evaluated you can diagnose a condition or recommend treatment. Do not start, stop, or change a medication without talking to the clinician who prescribes it.