If you are in crisis: Samaritans 116 123 (free, 24/7), text SHOUT to 85258, NHS 111, or attend your nearest A&E.
What the regulator says
The MHRA Drug Safety Update of 29 April 2024 ("Finasteride: reminder of the risk of psychiatric side effects and of sexual side effects (which may persist after discontinuation of treatment)") explicitly lists psychiatric reactions among the risks patients must be counselled on. The MHRA further strengthened these warnings in a Drug Safety Update on 11 May 2026 and extended precautionary advice to dutasteride. Patient alert cards were introduced into finasteride packs as part of these updates.
In plain English
"Brain fog" is not a specific medical diagnosis but a cluster of symptoms patients describe: difficulty concentrating, slowed thinking, word-finding problems, mental fatigue. On finasteride, these symptoms have been reported by a minority of users and feature in the psychiatric reactions the MHRA flagged in 2024. Mechanistically, finasteride blocks 5-alpha-reductase, which also has roles in the brain (neurosteroid synthesis); whether this explains the symptom in every reporter is not settled. The lived experience is real; the precise biology is still being studied.
How long does it last
In most cases reported in the regulator's case series, symptoms resolved within weeks of stopping the medication. The MHRA explicitly recognises that in a small number of cases psychiatric symptoms have been reported to persist after discontinuation. There is no formula for predicting which patients will experience persistence.
What to do if it happens to you
Contact your prescriber promptly. Document the symptoms (onset, severity, timing, what makes it better or worse). Your clinician will discuss whether to continue at the current dose, reduce, switch (e.g. to topical only) or stop. Reporting via the MHRA Yellow Card scheme contributes to the regulator's ongoing review.
When to seek urgent care
If brain fog is accompanied by suicidal thoughts, severe mood changes, or any symptom you find frightening, contact Samaritans on 116 123 (free, 24/7), NHS 111, or attend your nearest A&E immediately.
Want bloods to help investigate?
If you would like a bloodwork baseline to support the clinical conversation about your symptoms, our sister diagnostic service WMG Health offers panels designed around the question you are asking. A clinician-designed custom panel (from £275) is usually the best route when the question is specific.
Same Westminster Medical Group, single clinical record, results visible to your WMG Meds prescriber.