Finasteride and memory: what a rat study found

Memory or concentration problems since taking finasteride? In a 2021 study, rats given a high dose for a week made more mistakes in a memory maze and spent less time with other rats.

It’s a study in animals, so it can’t show that the same happens in people. It matters because problems with cognition are part of post-finasteride syndrome (PFS), and the UK medicines regulator warns that finasteride’s sexual side effects can last after stopping.

The study also found a change in a brain enzyme linked to memory. What does that mean for people who take finasteride?

Why would finasteride affect the brain?

Finasteride blocks an enzyme called 5-alpha reductase. That’s how it lowers DHT, the hormone behind male hair loss and an enlarged prostate.

The same enzyme is also a key step in making neurosteroids. These are steroids made in the brain that help it work, including allopregnanolone. The researchers start from this point: block the enzyme, and the brain may make less of them.

There’s some evidence from people too. A 2017 study of 16 men with PFS found changed levels of several of these steroids in the fluid around the brain and spinal cord. We’ve written about that study of neurosteroids in PFS separately.

What did the rat study do?

A team at the National Institute of Mental Health and Neuro Sciences in Bengaluru, India, ran the study. It was published in the journal Psychoneuroendocrinology.

They used young adult male rats. First the rats learnt a maze with eight arms, where food sits at the end of some of them. A rat that remembers the right arms makes fewer wrong turns.

Then the rats got either finasteride or a dummy injection every day for seven days. On day eight, the team tested whether the rats still remembered the maze.

A second test looked at social behaviour. Each rat could spend time with another rat or with an object. Then it could choose between a rat it had met before and a new one. Rats usually prefer the new one.

In a separate group, the researchers measured an enzyme called acetylcholinesterase in four brain areas.

What did the researchers find?

At the higher dose, the rats did worse on the maze. They made fewer correct choices and more errors, including errors that point to a memory problem.

The same dose changed social behaviour. The rats spent less time with the other rat compared with the object. They also spent about the same time with a familiar rat as with a new one.

In the brain, acetylcholinesterase was less active in three areas: the frontal cortex, the hippocampus and the septum. This enzyme breaks down acetylcholine, a chemical messenger the brain uses for learning and memory.

The authors suggest finasteride may affect cognition through this acetylcholine system. They also write that further studies are needed to understand the exact link.

What does a rat study tell us about people?

It tells us where to look, not what happens in people.

The doses were 30 and 100 mg per kilogram of body weight, injected under the skin. People take a 1 mg or 5 mg tablet a day. The rats got a much larger dose, by a different route, for one week.

The rats were tested the day after their last dose. So the study says nothing about whether any effect lasts after stopping, which is the question for people with PFS. The enzyme was also measured in different rats from the ones that did the tests.

In people, the evidence comes from a different direction. Doctors and researchers who proposed criteria for PFS in 2022 list cognitive problems, depression and suicidal thoughts among its effects. They note these can happen with or without sexual problems. The rat study offers one possible mechanism to test.

What can I do?

These medicines help many people. If you have side effects, that’s a decision for you and your prescriber.

In May 2026 the UK medicines regulator said finasteride is linked to depression and suicidal thoughts. It advised people on finasteride 1 mg to stop and contact their doctor if these happen. If you’re struggling, the Samaritans are on 116 123 in the UK.

If your memory or concentration changed on finasteride, tell your GP. Give your dates, such as “Finasteride 1 mg from March 2022, last tablet June 2023”, and how things were before.

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. If symptoms continued after stopping, write Post 5-alpha-reductase inhibitor syndrome (MedDRA 10082430).

Our reporting guide walks you through it

If cognition is one of your PFS symptoms, our guide to brain fog in PFS and PSSD has practical ideas from other patients.

Sources

1. Ahire A, Nair KP, Shankaranarayana Rao BS, Srikumar BN. The potential involvement of cholinergic system in finasteride induced cognitive dysfunction. Psychoneuroendocrinology 2021;124:105066. Male Wistar rats aged 2 months; vehicle or finasteride 30 or 100 mg/kg subcutaneously for 7 days; tests on day 8; effects reported at 100 mg/kg; acetylcholinesterase measured in a separate group.
2. Melcangi RC, Santi D, Spezzano R and colleagues. Neuroactive steroid levels and psychiatric and andrological features in post-finasteride patients. J Steroid Biochem Mol Biol 2017;171:229-35.
3. 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. Section 5, post-finasteride syndrome.
4. MHRA, Finasteride and dutasteride: updated safety warnings for psychiatric side effects and sexual dysfunction, Drug Safety Update volume 19, issue 10, 11 May 2026.