Brain fog at 20: could a medicine be why?

Brain fog at 20 often has an everyday cause, such as poor sleep, stress or low mood. Some people say trouble with concentration and memory began on an antidepressant, the hair-loss medicine finasteride or the acne medicine isotretinoin, and stayed after they stopped. This has names: post-SSRI sexual dysfunction (PSSD), post-finasteride syndrome (PFS) and post-Accutane syndrome (PAS).

They’re about more than sex. Doctors and researchers who agreed a checklist to recognise them in 2022 list trouble with concentration and memory among the symptoms. After finasteride or isotretinoin, they write, it can come with no sexual problems at all.

To count as PSSD, the checklist also needs a lasting change in how the genitals feel, often numbness. It lists feeling emotionally numb too.

Sumair was 21 and at college when he tried finasteride on his scalp for slight thinning. He used it four times. In the months after he stopped, he says, problems with memory and focus arrived, along with sexual problems and insomnia.

Play video: Sumair on life at 21 after topical finasteride

Before, he says, he was “pretty much a normal 21 year old”. Almost five months after stopping, he’d moved back home and was studying online.

What causes brain fog in your 20s?

Often something ordinary. The NHS says memory problems are “often nothing serious”, and names stress, anxiety, depression and sleeping problems as common causes that can be treated.

The NHS also lists:

• Long COVID. Problems with memory and concentration, “also called brain fog”, are among its commonest symptoms.
• Something a blood test can find. An underactive thyroid can make it hard to concentrate. Low vitamin B12 can affect memory.

The NHS says to see a GP if memory problems affect your daily life. A London hospital’s guide for young people with long-term tiredness has tips for coping with fog at school and in exams.

Can medication cause brain fog?

Yes, some can affect concentration while you take them. Your leaflet’s list of side effects is the first place to look.

Three stand out, because some people say their fog didn’t lift when they stopped:

• SSRI and SNRI antidepressants, such as sertraline or duloxetine, used for depression and anxiety. The UK sertraline leaflet lists “lack of attention” as common (up to 1 in 10 people).
• Finasteride, sold as Propecia. Its UK leaflet lists depression and anxiety, but not memory or concentration.
• Isotretinoin, sold as Roaccutane. Its UK leaflet says drowsiness is very rare, and says nothing about memory or concentration.

None of the three leaflets says trouble with concentration or memory can continue after stopping, so the medicine might never cross your mind.

Can brain fog last after stopping a medicine?

Some people say it does. In 2025 the US medicines regulator put out a warning about finasteride used on the skin, the way Sumair used it. Reports sent to it included brain fog, and most said the problems carried on after stopping.

In one study in Boston, men with lasting sexual symptoms after finasteride said they had more trouble with cognition than other men, but scored normally on tests. For isotretinoin, when we searched in October 2026, we found no study that tested memory more than two months after treatment ended. Our page on Accutane brain fog covers what’s been studied.

Nobody has measured how often it happens. For some people it has lasted years after stopping. Nobody knows yet who will be affected, or whether it will ease.

Benjamin took the antidepressant duloxetine (Cymbalta) for a month at 27. Almost 14 years on, when someone gives him directions, he has to start again and again. “Only a little bit of information can come through at once,” he says.

Play video: Benjamin on taking in information after duloxetine

How can I tell if it’s the medicine?

On your own, you can’t be sure. Start with the order of events.

Three things to write down

Before

How you wereYour concentration and memory before the medicine.

On it

When it changedThe month the fog began, and your dose.

After

What stayedWhether it's still there months after your last dose.

The 2022 checklist works the same way. The problem wasn’t there before the medicine. It’s still there three months or more after stopping. And no other illness or medicine explains it. So ruling out the everyday causes is part of the answer. Our guide on how to tell if a medicine caused it goes further.

These medicines help many people. If you have side effects, that’s a decision for you and your prescriber. Don’t stop an antidepressant suddenly. For finasteride and isotretinoin, follow what the leaflet says.

Take a note to your GP: “Sertraline 50 mg from January 2024, last tablet June 2024. Since March I lose my place when I read. I sleep eight hours. None of this before 2024.”

Report it: it helps everyone

A doctor’s note helps you. A report to the medicines regulator helps everyone else: it is how patterns get noticed.

• No proof needed. A suspicion is enough, even years after stopping.
• Where: the Yellow Card scheme in the UK, MedWatch in the US.
• Use the right words. Describe the brain fog in plain words. If symptoms continued after stopping, write Post-SSRI sexual dysfunction (MedDRA 10086208) for an SSRI or SNRI, or Post 5-alpha-reductase inhibitor syndrome (MedDRA 10082430) for finasteride. For isotretinoin there’s no term yet, so say the symptoms continued after stopping.

Our reporting guide walks you through it

What else do people ask?

Could it just be the anxiety or depression I was treated for? It could. The NHS says anxiety can make it hard to concentrate, and depression can make decisions hard. That’s why your dates matter: when your mood changed, and when the fog began.

Does brain fog from a medicine go away? The leaflets say many side effects go once you stop, but not all. The Roaccutane leaflet calls them “generally reversible”, and adds that “some may continue after treatment has stopped”. For Benjamin, the fog was “crippling” for the first two or three years. He still struggles to take in new information.

I already have PSSD, PFS or PAS. What helps? Our page on brain fog in PFS and PSSD shares what people say helps them get through the day. Read more about PSSD, PFS and PAS.

When Sumair first told a doctor, she said his symptoms were probably psychosomatic, caused by the mind. If your fog began on an antidepressant, finasteride or isotretinoin, you can report it without a doctor agreeing.

Sources

1. NHS, Memory loss (amnesia), page last reviewed 9 October 2023. “It’s often nothing serious, but it’s best to get checked.” Common, treatable causes: “stress”, “anxiety or depression”, “sleeping problems (insomnia)”. See a GP if “memory problems are affecting your day-to-day life”.
2. NHS, Generalised anxiety disorder, last reviewed 22 October 2024: “finding it difficult to concentrate”. NHS, Depression in adults: symptoms, last reviewed 5 July 2023: “finding it difficult to make decisions”.
3. NHS, Long COVID, last reviewed 19 August 2025: among the most common symptoms, “problems with your memory and concentration, also called brain fog”.
4. NHS, Underactive thyroid, last reviewed 28 April 2025: “difficulty concentrating”, diagnosed with a blood test. NHS, Vitamin B12 or folate deficiency anaemia: symptoms, last reviewed 20 February 2023: “problems with memory, understanding and judgment”.
5. University College London Hospitals NHS Foundation Trust, Understanding and managing brain fog: for young people living with fatigue conditions. Coping tips for school and exams, including “See if you can be given extra time in exams and extensions for assignments”. Written for young people with fatigue conditions.
6. Healy D, Bahrick A, Bak M and colleagues. Diagnostic criteria for enduring sexual dysfunction after treatment with antidepressants, finasteride and isotretinoin. Int J Risk Saf Med 2022;33(1):65-76. Proposed criteria agreed by an expert panel, not an official diagnosis. PSSD: the necessary criterion is an enduring change in genital sensation; ancillary symptoms “may include” emotional numbing and “cognitive impairment”. For finasteride and isotretinoin, effects “that can occur independently of any sexual difficulties” include “cognitive impairment”. All three: problem present “for ≥3 months after stopping treatment”, none before the drug, and no current medical condition or medicine that could account for it. “The incidence of these conditions is unknown.”
7. US Food and Drug Administration, FDA alerts health care providers, compounders and consumers of potential risks associated with compounded topical finasteride products, content current as of 22 April 2025. Reports from 2019 to 2024 describe adverse events including “brain fog”. “Most of the reports FDA has received state the adverse events continued to persist after product discontinuation.” About compounded products for the skin, not Propecia tablets. A count of reports, not a rate.
8. Lustral (sertraline), patient leaflet, Electronic Medicines Compendium (EMC 2835), last revised December 2025. Section 4, common (up to 1 in 10 people): “lack of attention”. Uncommon: “amnesia”. Its warning that symptoms “have continued after stopping treatment” is about sexual problems.
9. Propecia 1 mg, patient leaflet (UK, EMC 2194), last revised May 2026. Section 2: mood alterations and depression. Section 4: “Some of the side effects are temporary with continued treatment or disappeared when treatment is stopped”; anxiety listed. No mention of memory or concentration.
10. Roaccutane, patient leaflet (UK, EMC 100633), last revised April 2026. “Drowsiness and dizziness have been reported very rarely.” Side effects “are generally reversible after changing the dose or stopping treatment, however some may continue after treatment has stopped.” No mention of memory or concentration.
11. Basaria S, Jasuja R, Huang G and colleagues. Characteristics of men who report persistent sexual symptoms after finasteride use for hair loss. J Clin Endocrinol Metab 2016. Abstract: symptomatic former users had “more cognitive complaints” than the other groups “but had normal objectively assessed cognitive function”. One centre in Boston.
12. Our PubMed search on 28 October 2026: isotretinoin with cognitive, memory, cognition or neuropsychological terms, 19 results. The latest retest of memory in people was two months after a course: Ormerod and colleagues, Psychopharmacology 2012.
13. Moral Medicine, Just 4 Doses of Topical Finasteride Changed His Life, interview with Sumair (spelled Sumer in the title), 6 April 2023. From the YouTube auto-captions: 21 and a college student (0:40). Memory problems, insomnia and “problems with focus” (6:12 to 6:18). His GP said it “was probably psychosomatic” (6:59 to 7:01). About five months since stopping (7:51). “Memory and focus” among his symptoms (8:31), “pretty much a normal 21 year old” (8:51), school online and back home (9:07 to 9:13). Embedded as an extract from 8:24 to 9:21. His story on our site: Sumair’s story.
14. Moral Medicine, Benjamin’s 14-Year Battle with PSSD, 16 July 2024. From the YouTube auto-captions: 27 when it began, in 2011 (2:18). “Almost 14 years” (1:46). A month on the medicine (3:55), named as Cymbalta by the channel and his story page. “For the first two or three years the brain fog was immeasurable… it was crippling” (5:42 to 5:51). “I still have a sensory processing delay” with directions, and “only a little bit of information can come through at once” (24:46 to 25:26). Embedded as an extract from 24:46 to 25:25.

Sources checked on 28 October 2026. AI-assisted writing and review, not clinical review.