Did a medicine cause this? 3 ways to tell

Doctors judge if a medicine like an antidepressant caused a side effect by asking when it started, what else could explain it and what happened after stopping. You can report without being sure, and problems lasting after stopping, as in PSSD, PFS and PAS, don’t rule the medicine out.

Doubt stops many people from saying anything. Knowing how the judgement is made helps you give your doctor, and the regulator, the details they need.

Katie took fluoxetine (Prozac) for about three years. Sex and feelings changed, and she went back to her GP several times. Nobody told her it could be a side effect, she says.

Play video: Katie on PSSD after Prozac

After she stopped, doctors put the problems down to low self-esteem, trauma and depression. She’d had all three before the medicine. “I didn’t have any problems with sex, attraction, or emotional connection before the medication,” she says. She only made the link herself years later.

How do doctors decide if a medicine caused a side effect?

They weigh the same few questions, usually without a test to settle it. The World Health Organization’s causality guide asks about timing, other causes and what happened after stopping. It sorts each case from “certain” down to “unlikely”.

It’s frank about its limits, too. The method can’t “change uncertainty into certainty”, it says.

1

Timing

Did it start after the medicine, at a time that makes sense?

2

Other causes

Could an illness or another medicine explain it as well?

3

After stopping

What happened when the medicine was stopped?

Timing comes first. A problem that began after the first dose points one way. One that was there for years before points the other.

Sumair’s timing was hard to miss. He used topical finasteride four times. Almost at once, he says, he felt burning in his genitals. It eased after he stopped, but new sexual problems followed.

Play video: Sumair on four doses of topical finasteride

Timing is often less clear than that. Katie only noticed the sexual changes over time, because she was single when she started. Write down your dates as well as you can. A year and a month is fine.

Could it be something else?

Sometimes, and a good doctor will ask. Depression, other illnesses and other medicines can all affect sex, mood and energy. If one of them explains it just as well, the WHO guide calls the link “possible” rather than “probable”.

The key is what you were like before. The 2022 criteria for PSSD ask for no sign of the same sexual problem before the drug. They also say a mental health diagnosis doesn’t rule PSSD out.

Katie’s case turns on exactly that. Our article on PSSD or depression goes through the differences.

What if it didn’t go away when I stopped?

Then the usual scoring doesn’t fit you well. Some doctors use a points score published by Naranjo and colleagues in 1981. It gives a point if the problem got better when the drug was stopped. If it didn’t, that question scores nothing.

The 2022 criteria address this directly. Their authors write that stopping and restarting the drug to see what happens “is not suitable” for side effects that last or get worse after stopping.

UK leaflets for SSRIs, finasteride and isotretinoin now warn that some sexual problems have continued after stopping. So a problem that stayed doesn’t rule the medicine out. For these conditions, it’s the very thing the leaflets describe.

What can I do?

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.

When you see your GP, bring your answers to the three questions:

1. Your medicine and dates: “Sertraline 50 mg from January 2023, last tablet March 2024.”
2. When it started: before, while taking it, or after stopping.
3. How it was before, and anything else you took: “No problems before 2023. No other medicines.”
4. What happened after stopping, in your own words, with dates.

Many people say it took time to be taken seriously. Bring the leaflet line. You can report it without a doctor agreeing.

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-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?

Do I need to be sure before I report it? No. The UK regulator, the MHRA, said in November 2023: “You don’t have to prove that the healthcare product caused the side effect.” The US reporting form says to report even if you’re “not certain”. You can also report a side effect years later.

Can a doctor test whether a medicine did it? Usually not. The WHO guide says such tests are mostly absent, and that taking the drug again to see what happens is rarely ethical. For PSSD, our page on blood tests explains what tests can rule out.

What if I took more than one medicine? That makes it harder to pin on one, and your doctor will ask about each. Report it anyway. List every medicine you took, with its dose and dates, so the regulator can match your report with others.

Katie spent years thinking something was wrong with her. If you’ve noticed a change since a medicine, report it: a suspicion is enough.

Sources

1. World Health Organization and Uppsala Monitoring Centre, The use of the WHO-UMC system for standardised case causality assessment, published 5 June 2013. Most case reports concern suspected reactions; reactions are “rarely specific for the drug, diagnostic tests are usually absent and a rechallenge is rarely ethically justified”; “In practice few adverse reactions are ‘certain’ or ‘unlikely’”. Table 1: causality assessment cannot “Prove the connection between drug and event” or “Change uncertainty into certainty”. Table 2: “Probable / Likely” needs a reasonable time relationship and a response to withdrawal that is “clinically reasonable”. It must be “Unlikely to be attributed to disease or other drugs”. “Possible” applies when the event “Could also be explained by disease or other drugs” and information on withdrawal “may be lacking or unclear”.
2. Naranjo CA, Busto U, Sellers EM and colleagues. A method for estimating the probability of adverse drug reactions. Clin Pharmacol Ther 1981;30(2):239-45. Ten questions; question 3, “Did the adverse reaction improve when the drug was discontinued or a specific antagonist was administered?”, scores +1 for yes and 0 for no or do not know. Totals: 9 or more definite, 5 to 8 probable, 1 to 4 possible, 0 or less doubtful. Question wording and scores as reproduced in Ghosh S, Bhuyan D, Clin Psychopharmacol Neurosci 2017;15(2):187, table 1.
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. PSSD criteria 7 to 9: no evidence of pre-drug sexual dysfunction matching the current profile, and no current medical condition, medication or substance misuse that could account for the symptoms. A mental health diagnosis “does not prevent a diagnosis of these enduring conditions”. On causality: “The challenge-dechallenge-rechallenge strategy which is sometimes used to assess whether an effect is linked to a medication is not suitable for investigating adverse effects that persist or worsen after a medication is stopped.”
4. MHRA, Suspect you have experienced a side effect or incident from a healthcare product? Submit a Yellow Card report to improve safety for everyone, press release, 6 November 2023: “You don’t have to prove that the healthcare product caused the side effect or incident - just a suspicion is enough for you to submit a report.”
5. US Food and Drug Administration, Form FDA 3500, MedWatch voluntary reporting form for health professionals, version 09/2025: “Report even if: You’re not certain the product caused the event; You don’t have all the details”.
6. Moral Medicine, I Lost My Sexual Identity After Prozac, interview with Katie, 26 May 2026 (the title is the channel’s). Quotes from the YouTube captions: GP visits while on fluoxetine (4:04); doctors attributing her problems to low self-esteem, trauma and depression after stopping (4:50); “I didn’t have any problems with sex, attraction, or emotional connection before the medication” (5:04). The sexual changes were not noticeable at first because she was single (2:37 to 2:44); she realised over time (3:06). Her story on our site: Katie’s story: 14 years after Prozac.
7. Moral Medicine, Just 4 Doses of Topical Finasteride Changed His Life, interview with Sumair, 6 April 2023 (the title is the channel’s). Our page plays an extract, 3:33 to 5:22; the views are his own. Four applications of topical finasteride (3:41); genital burning “almost immediately” (3:43); the burning went away after stopping (4:30); new sexual dysfunction was the first new symptom as he stopped (5:06 to 5:12). Quotes from the YouTube captions.
8. MedDRA terms as listed in our reporting data: Post-SSRI sexual dysfunction (10086208) and Post 5-alpha-reductase inhibitor syndrome (10082430). There is no term yet for lasting effects after isotretinoin.