Skip to main content
Tessa NewsLink
Paste a health news link, or browse

Source study found

Story checked

Your Body Keeps Producing Cannabis-Like Chemicals Throughout a Marathon : ScienceAlert (opens in a new tab)

sciencealert.com · 2026-09-09

Short answerEvidenceSource

Short answer

Mixed

Mixed.

The claims we could check match the study, but some claims were not covered by the evidence reviewed.

  • 3 supported
  • 4 not covered

Checked against the study summary. The full text wasn't available, so some details couldn't be settled either way.

Share this check

Follow the evidence trail
1
2

NewsLink checks it

Mixed

Every claim we could check holds up. Three of seven claims match the study. This overall rating is based only on the claims we could check. Four claims the study doesn't address.

  • 3 supported
  • 4 not covered
Open claim evidence
3
Source paper

Source layer

The 3 papers the story cites

Source study separated from background citations.

The research anchor for the report.

Then inspect each claim

Evidence layer

Claim by claim

Each claim gets a verdict. Expand it to see the evidence directly below.

7 claims in this story

Showing all 7 claimsChoose a verdict to focus the list.

Claim 1 of 7Not coveredResearchers led by first author Michael Siebers of the University of Duisburg-Essen conducted two field studies with experienced endurance runners, including 19 marathon participants and 36 ultramarathon athletes.View evidenceHide evidence

As stated19 participants; 36 athletes; 100, 160, or 230 kilometers

Why this verdict

The participant counts and race distances are supported by the profile: 19 trained runners in Study 1 and 36 ultramarathon runners in Study 2 over 100/160/230 km. However, the supplied abstract-level profile does not verify the first author, institutional affiliation, or leadership framing.

1

Study evidence

Plasma anandamide (AEA) concentrations increased progressively throughout the marathon and remained elevated after a 45-minute recovery; the duration-matched walking session produced only modest/gradual AEA changes.

“In Study 1, 19 trained runners completed both a marathon and a duration-matched walking session, with repeated blood sampling every 14 km during the marathon and after a 45-minute recovery.”
2

Study evidence

Anandamide (AEA) concentrations increased post‑race compared with baseline across all ultramarathon distances (100 km, 160 km, 230 km).

“In Study 2, 36 ultramarathon runners completed races of 100 km, 160 km, or 230 km and provided blood samples before and after their respective races.”
Claim 2 of 7Not coveredDuring the marathon, anandamide in blood steadily increased, becoming significantly higher from 14 kilometers onward than during a matched walk and remaining elevated 45 minutes after the finish.View evidenceHide evidence

As statedfrom 14 kilometers onward; 45 minutes after the finish

Why this verdict

The profile supports that plasma anandamide increased progressively during the marathon and remained elevated after 45 minutes of recovery, with walking producing only modest/gradual changes. But the more specific claim that it was significantly higher than walking from 14 km onward is not available in the abstract-level profile.

1

Study evidence

Plasma anandamide (AEA) concentrations increased progressively throughout the marathon and remained elevated after a 45-minute recovery; the duration-matched walking session produced only modest/gradual AEA changes.

“In Study 1, 19 trained runners completed both a marathon and a duration-matched walking session, with repeated blood sampling every 14 km during the marathon and after a 45-minute recovery.”
Claim 3 of 7Not coveredCompared with walking, marathon running was associated with greater happiness and lower anxiety, while pain increased significantly after 28 kilometers.View evidenceHide evidence

As statedafter 28 kilometers

Why this verdict

The profile supports the direction of the affective findings: marathon running was associated with higher euphoria/happiness and lower anxiety than walking, and pain increased after about 28 km. However, the claim’s use of 'significantly' for the pain increase is not verifiable from the abstract-level profile, which lacks p-values or detailed statistical metrics.

1

Study evidence

Plasma anandamide (AEA) concentrations increased progressively throughout the marathon and remained elevated after a 45-minute recovery; the duration-matched walking session produced only modest/gradual AEA changes.

“In Study 1, 19 trained runners completed both a marathon and a duration-matched walking session, with repeated blood sampling every 14 km during the marathon and after a 45-minute recovery.”
2

Study evidence

During the marathon (Study 1), runners reported higher euphoria and lower anxiety compared with a duration-matched walking session.

“Euphoria, anxiety, and pain were assessed as core features of the runner's high using visual analog scales.”
Claim 4 of 7Not coveredIn the ultramarathon study, levels of both anandamide and 2-AG increased after races of 100, 160, and 230 kilometers, but longer distance did not necessarily mean a bigger increase.View evidenceHide evidence

As stated100, 160, or 230 kilometers

Why this verdict

The profile supports that AEA and 2-AG increased post-race across ultramarathon distances of 100, 160, and 230 km. It does not provide enough abstract-level detail to verify the additional claim that longer distance did not necessarily mean a larger increase.

1

Study evidence

Anandamide (AEA) concentrations increased post‑race compared with baseline across all ultramarathon distances (100 km, 160 km, 230 km).

“In Study 2, 36 ultramarathon runners completed races of 100 km, 160 km, or 230 km and provided blood samples before and after their respective races.”
Claim 5 of 7SupportedA new BMC Medicine study investigated what happens to endocannabinoids when people run for several hours or longer.View evidenceHide evidence

Why this verdict

The abstract-level profile supports that the paper studied circulating endocannabinoids during prolonged endurance running, including a marathon with repeated sampling and ultramarathons of 100, 160, and 230 km.

1

Study evidence

Plasma anandamide (AEA) concentrations increased progressively throughout the marathon and remained elevated after a 45-minute recovery; the duration-matched walking session produced only modest/gradual AEA changes.

“In Study 1, 19 trained runners completed both a marathon and a duration-matched walking session, with repeated blood sampling every 14 km during the marathon and after a 45-minute recovery.”
2

Study evidence

Anandamide (AEA) concentrations increased post‑race compared with baseline across all ultramarathon distances (100 km, 160 km, 230 km).

“In Study 2, 36 ultramarathon runners completed races of 100 km, 160 km, or 230 km and provided blood samples before and after their respective races.”
Claim 6 of 7Supported2-AG rose near the end of the marathon and remained elevated during recovery.View evidenceHide evidence

As statednear the end; during recovery

Why this verdict

The profile states that plasma 2-AG increased during the later stages of marathon running and into early recovery, and that this pattern was not seen during walking.

1

Study evidence

Plasma anandamide (AEA) concentrations increased progressively throughout the marathon and remained elevated after a 45-minute recovery; the duration-matched walking session produced only modest/gradual AEA changes.

“In Study 1, 19 trained runners completed both a marathon and a duration-matched walking session, with repeated blood sampling every 14 km during the marathon and after a 45-minute recovery.”
Claim 7 of 7SupportedThe article says elevated endocannabinoid levels alone are not sufficient to produce a runner’s high, and that the study cannot prove these chemicals caused the psychological changes because they were measured in blood rather than directly in the brain.View evidenceHide evidence

Why this verdict

The profile supports the causal caveat: the studies are observational and measured peripheral plasma endocannabinoids, which may not directly reflect central nervous system signaling. It also supports the complexity point because ultramarathon eCB levels increased while post-race euphoria did not significantly change, consistent with the statement that elevated circulating endocannabinoids alone are not sufficient to establish a runner’s high.

1

Study evidence

Plasma anandamide (AEA) concentrations increased progressively throughout the marathon and remained elevated after a 45-minute recovery; the duration-matched walking session produced only modest/gradual AEA changes.

“In Study 1, 19 trained runners completed both a marathon and a duration-matched walking session, with repeated blood sampling every 14 km during the marathon and after a 45-minute recovery.”
2

Study evidence

Anandamide (AEA) concentrations increased post‑race compared with baseline across all ultramarathon distances (100 km, 160 km, 230 km).

“In Study 2, 36 ultramarathon runners completed races of 100 km, 160 km, or 230 km and provided blood samples before and after their respective races.”
Then look for missing context

Context layer

What the story left out

Important study details the story did not include.

  • Study 2 affective findings: after ultramarathons, pain increased, anxiety decreased, and euphoria did not significantly change from pre- to post-race.

    The story mentions the complexity of runner’s-high interpretation and notes that ultramarathon happiness was measured only before and after, but it does not fully reflect the reported ultramarathon affective pattern, especially increased pain and reduced anxiety.

    From observational repeated-measures (field)

  • Measurement limitation for affective outcomes: euphoria, anxiety, and pain were self-reported on visual analog scales and may be influenced by context or reporting bias.

    The story’s caveats mention pre/post timing for ultramarathon happiness but do not acknowledge the subjective self-report nature or potential reporting/context bias of the affective measures.

    From observational repeated-measures (field)

7 things the story did carry across
  • Study 1 design: 19 trained runners completed both a marathon and a duration-matched walking session, with repeated venous blood sampling every 14 km and after 45 minutes of recovery; plasma lipids were quantified by LC/MRM.
  • Study 1 biomarker findings: AEA increased progressively during the marathon and remained elevated after recovery; 2-AG rose later and into early recovery, with different temporal patterns from walking.
  • Study 1 affective findings: marathon running was associated with higher euphoria, lower anxiety, and increased pain after about 28 km compared with walking.
  • Study 2 design and biomarker findings: 36 ultramarathon runners in 100, 160, and 230 km races provided pre/post blood samples; AEA and 2-AG were elevated post-race across distances.
  • Causal limitation: observational field data and peripheral plasma measurements cannot prove that endocannabinoids caused psychological changes or directly represent brain endocannabinoid signaling.
  • Sample-size/generalizability limitation: Study 1 had 19 trained runners and Study 2 had 36 ultramarathon runners across multiple distances, limiting precision and generalizability to other populations.
  • Ultramarathon temporal-resolution limitation: ultramarathon affective data were pre/post only, so within-race or transient runner’s-high episodes may not have been captured.
Then read the study layer

Study layer

Study at a glance

Scan the study first. Expand only the parts you want to inspect.

Pieces of work

3

Evidence read

study summary

Lead result

human in vivo

1Lead resulthuman in vivoCharacterize the temporal dynamics of circulating endocannabinoids and related lipids during prolonged endurance running (marathon) and into short-term recovery, with an active comparator (duration-matched walking).Within-subject field study: marathon versus duration-matched walkingExpand

In plain English

In a within-subject field study of 19 trained runners, plasma endocannabinoids and related lipids were measured repeatedly during a marathon (samples every 14 km) and after a 45-minute recovery, and compared with a duration-matched walking session. Anandamide (AEA) increased progressively across the marathon and remained elevated after 45 minutes; walking produced only modest/gradual AEA changes. 2-arachidonoylglycerol (2-AG) rose during the later stages of the marathon and into early recovery (an effect not seen during walking). Marathon running was associated with greater euphoria and lower anxiety versus walking, while pain increased after ~28 km.

Key findings

  • Plasma anandamide (AEA) concentrations increased progressively throughout the marathon and remained elevated after a 45-minute recovery; the duration-matched walking session produced only modest/gradual AEA changes.
  • Plasma 2-arachidonoylglycerol (2-AG) rose during the later stages of marathon running and into early recovery; this stage-dependent increase was not observed during walking.
“In Study 1, 19 trained runners completed both a marathon and a duration-matched walking session, with repeated blood sampling every 14 km during the marathon and after a 45-minute recovery.”
What this piece can’t prove
  • Study 1 sample size was 19 trained runners (limiting precision and generalizability).
  • Field exercise protocol yields discrete sampling (every 14 km) rather than continuous measurement, providing limited temporal resolution between sampling points.
  • Biomarkers reported are peripheral (plasma) concentrations; peripheral changes may not directly reflect central nervous system endocannabinoid signaling.
2human in vivoTest whether endocannabinoid and related lipid concentrations change from pre- to post-race across ultramarathon distances (100 km, 160 km, 230 km).Study 2: ultramarathon pre/post field observational samplingExpand

In plain English

Study 2: field pre‑ vs post‑race sampling in 36 ultramarathon runners (100 km, 160 km, 230 km) quantified plasma anandamide (AEA), 2-AG, 1-AG, arachidonic acid (AA), and PEA by standardized LC/MRM. The abstract reports that AEA was increased post‑race across all distances; 2-AG was elevated post‑race across all distances consistent with a delayed/recovery‑related response. The abstract does not report numerical effect sizes, per-distance sample sizes, or explicit results for 1-AG, AA, or PEA.

Key findings

  • Anandamide (AEA) concentrations increased post‑race compared with baseline across all ultramarathon distances (100 km, 160 km, 230 km).
  • 2‑arachidonoylglycerol (2‑AG) concentrations were elevated post‑race across all ultramarathon distances, described as a delayed/recovery‑related response.
“In Study 2, 36 ultramarathon runners completed races of 100 km, 160 km, or 230 km and provided blood samples before and after their respective races.”
What this piece can’t prove

3 further details could not be confirmed from the summary.

3human in vivoDescribe acute affective responses (euphoria, anxiety, pain; runner’s-high features) during marathon running versus walking, and pre- to post-ultramarathon.observational repeated-measures (field)Expand

In plain English

In two field studies using self-report visual analog scales (VAS), marathon running (within-subject contrast vs a matched walking session) was associated with greater euphoria and lower anxiety and with increased pain emerging after ~28 km. In separate ultramarathon runners (pre/post race), ultramarathon completion was associated with increased pain and decreased anxiety, while euphoria did not change significantly post-race.

Key findings

  • During the marathon (Study 1), runners reported higher euphoria and lower anxiety compared with a duration-matched walking session.
  • Pain increased during marathon running, with an increase observed after ~28 km.
“Euphoria, anxiety, and pain were assessed as core features of the runner's high using visual analog scales.”
What this piece can’t prove
  • Affective outcomes were measured via self-report VAS, which are subjective and may be influenced by context and reporting bias.
  • Abstract provides directionality but no numeric effect sizes, confidence intervals, or detailed statistical metrics for the reported affective changes.
  • Sample sizes are moderate (Study 1 n=19; Study 2 n=36 across multiple race distances), potentially limiting precision and generalizability.
  • Participants were trained runners (Study 1) or ultramarathon participants (Study 2), which may limit generalizability to recreational or untrained populations.

1 further detail could not be confirmed from the summary.

Finally, the search trail

Method layer

NewsLink found the paper. Tessa takes you deeper.

NewsLink checks the story. Tessa is where you inspect the paper, authors, evidence, and research context.

Papers considered

The selected paper, plus nearby candidates.

Crossref, PubMed, Europe PMC · 17 candidate papers

And 11 more candidates considered.