The side effect reporting system misses most of what happens: median under-reporting 94 percent across 37 studies
"The median under-reporting rate across the 37 studies was 94% (interquartile range 82-98%)." For serious reactions the medians were still 80 to 95 percent.
Suggestive but preliminary. Not settled. how we score evidence
Caveat on this rating: Included studies span decades, 12 countries and very different methods, which is why the authors report medians and not a pooled rate. Not specific to psychiatric drugs or to the US system.
After approval, the main way regulators learn about a drug's harms is that someone chooses to file a report. This review asked how often someone does.
Significant findings
Hazell and Shakir (Drug Safety, 2006) found every study that compared adverse drug reactions detected by intensive monitoring with those actually reported to a national or regional system: "37 studies using a wide variety of surveillance methods were identified from 12 countries."
"The median under-reporting rate across the 37 studies was 94% (interquartile range 82-98%). There was no significant difference in the median under-reporting rates calculated for general practice and hospital-based studies."
Serious reactions fared little better. In general practice studies the median was "95% and 80%" for all and for more serious reactions; in hospital studies the rate for serious reactions "remained high (95%)"; and across 19 studies of specific serious reactions it "was still high at 85%."
The authors' conclusion: "significant and widespread under-reporting of ADRs to spontaneous reporting systems including serious or severe ADRs."
Worth asking
The studies are old and come from many countries, and reporting in the US today may be better or worse; nobody has measured it this way recently. But the FDA's system is still voluntary for clinicians and patients, and the logic has not changed: a problem that takes years to appear, in a person taking several drugs, is the least likely kind to be reported. That is how a long-term harm could be common and still officially rare. Patients can file a report with FDA MedWatch themselves. Almost nobody does.
Source
Under-reporting of adverse drug reactions: a systematic review — Hazell L, Shakir SA (2006)
Reputable peer-reviewed journal
Read the source: https://doi.org/10.2165/00002018-200629050-00003
DOI: 10.2165/00002018-200629050-00003
How this was scored
- Study design
- Systematic review of observational studies
- Funding
- Funding not disclosed
- Published in
- Reputable peer-reviewed journal
- Sample size
- not recorded
- Preregistered
- not recorded
- Conflicts disclosed
- not recorded
- Independent of proponent
- not recorded
- Retracted
- No
Read the full scoring rubric, including what it can't tell you.
Published September 21, 2026.
Questions
How strong is the evidence behind this?
veisund rates this source "early signal". Suggestive but preliminary. Not settled. It scores 52 out of 100 on our published rubric. One caveat travels with that badge: Included studies span decades, 12 countries and very different methods, which is why the authors report medians and not a pooled rate. Not specific to psychiatric drugs or to the US system. The score is calculated from recorded facts about the source — study design, funding, publication venue, sample size, preregistration — not typed in by an editor.
What is the source for this?
Under-reporting of adverse drug reactions: a systematic review — Hazell L, Shakir SA (2006). Published in: Reputable peer-reviewed journal. DOI: 10.2165/00002018-200629050-00003. The full source is linked on this page so you can read it yourself.
Who paid for this research, and does that matter?
Study design: Systematic review of observational studies. Funding: Funding not disclosed. Independence from the proponent is not recorded. Industry sponsorship is one of the most reliably measured biases in medicine, which is why funding carries real weight in the score rather than sitting in a footnote.
Is this medical advice?
This is information to bring to your prescriber, not medical advice and not a reason to change anything on your own. Nothing here is an instruction to stop or reduce a medication. If you are in crisis, call or text 988.
This is information to bring to your prescriber, not medical advice and not a reason to change anything on your own. Nothing here is an instruction to stop or reduce a medication. If you are in crisis, call or text 988.