Why This Matters

If you have migraine, you probably know which side of your head it tends to hit. Some people get them on the left every time. Others on the right. Some switch. Most are bilateral or shift around. It's one of those features patients notice and clinicians sometimes ask about.

Between 2023 and 2024, three papers came out asking whether left-sided and right-sided migraine are actually different conditions. They got picked up by patient podcasts and migraine communities. The claims spread quickly. Left-sided migraine was tied to anxiety, bipolar disorder, and PTSD. Right-sided migraine was linked to cognitive problems and changes in brain blood flow. White matter lesions on MRI were said to differ depending on which side hurt.

Those are big claims. If they hold up, they could change how migraine is diagnosed and treated. So I went back and read everything: all three papers, the full PhD dissertation they came from, and the public podcast where the lead author communicated the findings to patients.

What I found is a meaningful gap between what the data actually shows and what has been said about it. This post walks through that gap with the evidence.

The Three Studies, Briefly

Before getting into the problems, here is what was published by the same lead author.

On paper, this looks like progress. Three studies. A scoping review identifies hypotheses, follow-up work tests them. Each study reinforces the next. In practice, each one has problems significant enough to undermine its own conclusions, and those problems compound when the papers cite each other.

The Scoping Review: Foundation Built on Sand

The scoping review is the foundation. Every paper that came after it cites it to establish that left and right migraine are meaningfully different. So if the foundation is weak, everything built on top inherits that weakness.

Here is what those 26 studies actually look like in aggregate.

Every one of the 26 studies was observational. None of the findings have been replicated. The authors say so directly in the discussion: the differences they found are "often based on single studies, none of which have been replicated."¹ That sentence is buried in the discussion section. The conclusion of the abstract says the findings "raise the possibility that the pathophysiology of left- and right-migraine may not be identical." Those are not the same statement, and the abstract is what most people read.

The sample size problem

Here is what the studies behind the central claims actually look like.

Three subjects on one side. Six on the other. Studies with this little statistical power can produce essentially any result through chance alone. Treating their findings as evidence for differences between left and right migraine isn't a methodological limitation. It's a fundamental problem with the evidence base.

The unpublished thesis problem

One of the 26 sources isn't a journal article. It's an unpublished master's thesis from Concordia University, dated 2005.⁴ It appears in the main results table with the same formatting as every peer-reviewed paper. No flag. No asterisk. No note in the table that this source has never been independently peer reviewed.

That thesis is the primary source for the cognitive findings: claims about reduced executive function, attention problems, motor slowness, and visuospatial memory deficits in right-sided migraine. Those claims have circulated in the migraine community as if they were established. They aren't.

And the scoping review's own authors say this about that thesis, in their own paper:

The authors are saying, in their own published paper, that the findings from this source are likely partly spurious. This is a known statistical problem called multiple comparisons inflation. When you run enough tests, some will come up positive purely by chance.

And then the cognitive findings from that thesis are still in the results. They still feed into the conclusion. Including a source you've flagged as statistically unreliable, without quarantining its findings from the main analysis, misrepresents the evidence to anyone who reads the abstract or the table without working through the full discussion.

The mixed population problem

Two of the 26 studies were not migraine studies. Both used the same patient cohort, where the majority of subjects had headaches that weren't migraine. The cohort included tension-type headache and cluster headache patients. The inclusion criterion for those studies was that the headache was predominantly one-sided, not that it was migraine. These were included in a review specifically about migraine laterality, presented in the same results tables as migraine-specific studies.

The definition problem

If you look at the column in Table 1 labeled "Definition of Unilateral Migraine," the variation is striking. Some studies define left-sided migraine as the predominant headache side. Others require headache restricted to one side without crossing midline. One uses a laterality score. Another uses a single drawing exercise. Another requires 70 percent of attacks on the same side.

These are not comparable populations. Pooling their findings as if they describe the same condition produces noise rather than signal.

The Cross-sectional Study: When Your Own Data Disagrees

The cross-sectional study is where this body of work becomes self-contradictory. It's the most rigorous of the three studies. It uses real clinical data, validated psychiatric scales, and proper statistical correction for multiple comparisons.

It also fails to replicate the central psychiatric claims that the scoping review elevated.

Of 6,527 migraine patients, 340 qualified. That's 5.2 percent. The other 95 percent never made it into the study at all because their headaches weren't strictly side-locked enough.

The lead author has acknowledged publicly that this group represents about 5 percent of migraine patients, and that the findings are "more scientifically interesting than clinically relevant."⁵ That's an honest framing. It also did not make it into the abstracts of the published papers.

Beyond the population issue, here is what the study actually found about psychiatric outcomes. These are the claims that anchored the scoping review and reached patients through podcast interviews.

For context, the conventional threshold for statistical significance is p < 0.05. These p-values are not close. The scoping review's psychiatric associations did not survive testing in the same researcher's own larger, more rigorous study.

That is the most important scientific finding in this entire body of work. It also barely gets discussed in the cross-sectional paper, and it was not clearly communicated in the public podcast that came after.

What did survive: left-sided patients in this strictly side-locked group had 3.6 fewer headache-free days and 2.4 more severe headache days per month than right-sided patients. That's a real difference in headache burden, worth noting. But the psychiatric story (the anxiety, the bipolar disorder, the PTSD) is not supported by the lead author's own data.

The fMRI Study: Seven People

The fMRI study found something genuinely interesting at the bilateral level: decreased cerebrovascular reactivity in the medial pulvinar during migraine attacks. The pulvinar is involved in pain processing, light sensitivity, and the integration of sensory information. A finding there during migraine is worth investigating further.

The laterality claim is a different story. The study scanned 19 patients total, split into 12 left-sided and 7 right-sided. The conclusion of the paper is that the changes observed are "explained exclusively by right-migraine." That conclusion rests on the seven-person subgroup.

In neuroimaging, a subgroup analysis of seven people is not a finding. It's a hypothesis. Publishing it as a finding, with framing that the work "may ultimately lead to improved treatment," overstates what the data can support.

There is also a methodological issue the authors disclose, to their credit. For the first nine subjects enrolled, the gap between their ictal scan (during a migraine attack) and their interictal scan (between attacks) was one and a half to two years. Migraine burden, frequency, and severity can change substantially over that time. Comparing measurements from scans separated by two years introduces a confound that can't be corrected after the fact.

White Matter Lesions: The Claim That Doesn't Hold Up

There's a separate paper from the same lead author, also published in 2024 in the Journal of Neurology, looking at white matter hyperintensities (WMHs, sometimes called white matter lesions) and headache laterality.⁶ The paper claims that WMH distribution differs between left and right-sided migraine. It builds on the older literature claiming that WMHs are about four times more common in people with migraine than in controls.

That older literature has not held up.

This is the largest population-based study of its kind, and it directly contradicts the framing in the Sprouse Blum WMH paper. When you study migraine in the general population (rather than in tertiary headache clinics where the most severely affected patients are concentrated), and you adjust properly for the things that actually drive vascular brain changes, the migraine signal disappears.

A 2025 systematic review of WMH and migraine reached a similar conclusion from a different angle.⁸ The authors couldn't even perform a meta-analysis. The studies were too heterogeneous in imaging protocols, lesion quantification methods, and study design. Their bottom line: WMHs are sometimes seen in people with migraine, but the clinical significance is unclear.

So here's where we are in 2025:

• The largest, best-controlled population study to date found no association between migraine and WMHs after adjusting for confounders.
• A recent systematic review concluded the literature was too heterogeneous to draw firm conclusions.
• The strongest predictors of WMHs in studies that did find associations were vascular risk factors (age, hypertension, diabetes, right-to-left shunt), not migraine attack frequency, severity, or laterality.⁹

None of this supports the framing in the Sprouse Blum WMH paper that ties brain lesion patterns to which side of your head hurts. It also doesn't support the older "four times more common in migraine" claim, which has been overtaken by better evidence.

What Patients Took Away

I want to spend a moment on what happened after the podcast went out, because this is the part of the story that matters most. The podcast didn't stay in academic discussions. It reached patients. And the way patients absorbed it shows exactly why the communication gap I described above is not abstract.

Below are quotes from a r/migraine discussion thread where the podcast was shared and patients responded. These are unedited patient voices.

This is the textbook case of the harm I was worried about. A patient is identifying themselves with the unverified psychiatric profile from the scoping review. The conditions they list (GAD, PTSD, bipolar 2) are exactly the ones the cross-sectional study found no statistical association with in the same researcher's larger dataset. The p-values were 0.731, 0.766, and 0.879. The patient does not know that. They are pattern-matching themselves to a story the evidence has not held up.

Same pattern, opposite side. A patient is matching themselves to the unverified cognitive profile for right-sided migraine. That cognitive claim, remember, rests on a single unpublished thesis from 2005 that the original authors themselves flagged as likely partly the result of statistical noise. The patient is using it as the explanation for what they experienced yesterday at university.

Here a patient is constructing a personal causal narrative from the podcast framing. Trauma therapy moved their migraine to a different side. That is not a hypothesis the data supports. It is now a story this person tells about their own life, written on the spot, in response to a podcast that suggested left-sided migraine and PTSD might be linked. Another commenter wrote that they would "consider myself 'lucky' to only get right sided ones from now on." A patient is making a value judgment about their own disease based on a framing the evidence does not support.

This one is the most important. A patient is sharing what looks like an authoritative summary of brain lesion findings with the entire community. They pulled it from Google's AI overview, which itself was synthesizing the Sprouse Blum work. It is now circulating in r/migraine as if it were established fact.

The claim it makes is exactly the one the 2024 Rotterdam Study (4,920 participants, the largest population-based study to date) found no support for once cardiovascular factors were properly accounted for. But none of the patients reading that comment know that. They see a confident summary, with a percentage, presented in the voice of authority. They take it as settled.

This is the mechanism. Preliminary findings get communicated in a podcast without the caveats. They get summarized by AI tools. They get pasted into patient communities. They get repeated until they sound like consensus. By the time they reach a patient, all the scaffolding has fallen away and what is left is "left-sided migraine causes brain lesions."

That is not abstract harm. It is documented. It is happening. And it is happening in real time, in public, while the cross-sectional findings that contradict the original claims sit in a journal where almost no one outside academic neurology will read them.

The Citation Chain

There's a structural problem with this body of work that goes beyond any individual study. Each paper cites the one before it to establish the rationale for what follows. That creates the appearance of a growing body of evidence when what actually exists is a chain of studies, each inheriting the weaknesses of the one before it.

The scoping review identifies preliminary, unreplicated signals across 26 weak studies. The cross-sectional study cites the scoping review to justify its design, then fails to replicate the psychiatric associations. The WMH paper cites both to justify investigating laterality in brain imaging, building on a foundation where the behavioral associations have already collapsed in the lead author's own data. The fMRI paper cites all three.

By the time you reach the fMRI paper, the introduction reads as though a substantial body of evidence supports meaningful differences between left and right migraine. That impression comes from the citation chain. It doesn't come from replicated, robust, independently verified findings. And the citations within this body of work aren't independent verification, since they all come from the same lead author building on his own preliminary work.

This matters because other researchers will now cite these papers. Clinicians read abstracts. Patients encounter the claims summarized in podcasts and migraine communities. The further those claims travel from the original data, the more the caveats fall away and the conclusions harden into received wisdom.

The Pushback I Received

After raising these concerns publicly, I heard back from one person who knows the lead author personally. The arguments below came from that exchange. They're worth working through in this post because they represent the kinds of pushback that get used to deflect legitimate scientific critique. But I want to be direct about where they came from. These aren't anticipated defenses I'm pre-empting. They came from a single person with personal ties to the researcher, raised in response to the issues you've just read about.

That context matters. When the response to a documented methodological critique is private pushback rather than public engagement with the evidence, that itself is information.

What the Evidence Actually Shows

Pulling everything together, here is the honest version of what this body of work supports and what it doesn't.

If You're Living With This

If your migraine is strictly one-sided (always left, always right, never crossing midline), this research is at least about you. If your migraine switches sides, is sometimes bilateral, or is lateralized but not strictly unilateral, this research isn't about you. You're in the 95 percent the studies excluded.

If you've been carrying anxiety about which side your headache is on, about what it means for your MRI, your mental health, or your cognition, I want to be direct with you. The current evidence does not support those concerns. The largest population-based study to date found no association between migraine and brain structural changes once cardiovascular factors were properly accounted for. The psychiatric associations failed to replicate in the lead author's own larger study. The cognitive claims rest on a single unpublished thesis the authors themselves flagged as unreliable.

That's not a reassurance offered to make you feel better. It's what the data shows.

Notice which side your migraine attacks hit. Track it if it interests you. Mention it to your neurologist if you find it relevant. But don't let preliminary research with significant methodological limitations change how you understand your own disease.

Science moves forward by asking questions, including questions whose answers turn out to be less interesting than the preliminary data suggested. That's how the process works. What's a problem is when preliminary findings are communicated to patients as if they're settled, when failed replications aren't disclosed clearly, and when caveats that belong in the abstract end up buried in the discussion. - Cerebral Torque

Migraine patients have spent decades being dismissed and underserved by research. When new findings emerge, the community wants them to be real. That urgency is legitimate. It also creates vulnerability to overclaiming, which researchers, clinicians, and science communicators all share responsibility for protecting against.