Do THC and Alcohol Together Reduce Skeletal-Muscle Mitochondrial Respiration? What a Seven-Rat Experiment Actually Shows

Short answer: In an experiment using skeletal-muscle fibers removed from seven male rats, ethanol-containing laboratory solutions reduced mitochondrial oxygen consumption. Adding THC to the ethanol vehicle produced a significantly larger reduction in one specific preparation: gastrocnemius fibers from 12-week-old rats. That difference was not established in the 49-week-old gastrocnemius, and oxidative soleus muscle responded differently. The experiment did not administer alcohol and cannabis to living people, measure blood THC or blood alcohol, or test muscle strength, driving, psychomotor impairment, or an actual injury.

The original primary study is Charles and colleagues, published in Biology in December 2024: “Cannabis (THC) Aggravates the Deleterious Effects of Alcohol (EtOH) on Skeletal Muscles’ Mitochondrial Respiration: Modulation by Age and Metabolic Phenotypes” (DOI: 10.3390/biology13121080). Its most useful forensic lesson is about the distance between a controlled cellular readout and an individual human conclusion.

What did the researchers actually find?

The clearest comparison involved the predominantly glycolytic gastrocnemius muscle of young rats. At the highest reported experimental exposure, ethanol vehicle alone was associated with a 34.97% decrease in mitochondrial respiration relative to the preparation’s starting value, while the THC-in-ethanol condition was associated with a 49.92% decrease. The authors reported a statistically significant difference between those conditions (p < 0.05). Those are experimental oxygen-consumption changes, not percentages of human strength lost, increased collision probability, or an impairment scale.

In the older gastrocnemius preparations, the reported changes were −37.50% with ethanol alone and −31.79% with THC plus the ethanol vehicle. The study did not establish that adding THC significantly increased the ethanol-related reduction in that group. In soleus—the more oxidative muscle—the pattern also differed. Thus the result was neither uniform across ages nor interchangeable across muscle types.

Why does this matter to forensic toxicology?

Cannabis and alcohol are often discussed together in toxicology opinions. Yet evidence that a substance changes cellular respiration is not the same type of evidence as an analytically confirmed drug concentration, a behavioral test result, or a causal finding about a person. The study can inform a mechanistic hypothesis about mitochondrial physiology. It cannot identify whether a driver was impaired at a particular time, whether an injury resulted from the substances, or whether a measured blood result was clinically significant.

A case-specific review must keep biological matrices and the tested analyte separate from physiological mechanisms. For example, blood, plasma, serum, urine, oral fluid, hair and postmortem tissue have different analytical meanings. None was sampled from a human volunteer in this experiment.

Who—or what—was studied?

The researchers used muscle tissue from seven male Wistar rats: four aged 12 weeks and three aged 49 weeks. They excised two hindlimb muscles, gastrocnemius and soleus, after the animals were euthanized. These ages describe rat cohorts; they are not verified equivalents of a particular human’s age, health or drug sensitivity. Laboratory fiber runs were repeated, but repeated oxygen measurements are not additional independent animals.

Gastrocnemius contains a relatively greater proportion of glycolytic fibers, commonly adapted for high-power activity. Soleus is comparatively oxidative and rich in mitochondria. These are broad physiological characterizations, not proof that every individual fiber had the same metabolic profile. Comparing both muscles permitted the authors to ask whether the type of tissue modified the drug-solution response.

Crucially, this was an ex vivo tissue experiment. The rats did not undergo a controlled human-style drinking or cannabis-smoking session, and the investigators did not collect a post-exposure field-sobriety or locomotor examination from living animals.

How were ethanol and THC introduced?

Bundles of permeabilized, or “skinned,” muscle fibers were placed in a respiratory chamber. The investigators introduced successive concentrations of an ethanol-containing solution. In another condition, they introduced synthetic THC already dissolved in an ethanol vehicle. The reported highest chamber concentration was 0.2 × 10⁻³ mol/L THC in the THC/ethanol condition, while the corresponding ethanol-vehicle concentration in the ethanol-alone condition was 2.1 × 10⁻⁵ mol/L. The protocol stepped through five concentrations over about 20 minutes.

These are molar laboratory-chamber concentrations, not grams of beverage consumed, inhaled THC milligrams absorbed, blood-alcohol concentration, or a measured human plasma cannabinoid level. Converting them into a claimed number of drinks, legal BAC, or dose experienced by a driver would require assumptions and evidence that the experiment did not supply.

It also matters that THC was dissolved in ethanol. The investigators compared the combined THC/vehicle solution with the ethanol vehicle. They separately estimated the THC contribution by subtracting the ethanol-alone change from the combined change. That subtraction is an analytical attribution under an additive assumption; it is not a separately measured THC-only condition free of the ethanol vehicle. The distinction limits how confidently one can label a particular percentage as an independent pure-THC effect.

What was measured with the oxygen electrode?

The endpoint was mitochondrial oxygen consumption in permeabilized muscle fibers, measured with a Clark-type electrode. The researchers supplied glutamate and malate, then added ADP to stimulate complex-I-linked oxidative phosphorylation. Absolute baseline rates were reported as micromoles of oxygen consumed per minute per gram of dried muscle-fiber weight (µmol O₂/min/g dry weight). Subsequent drug-solution responses were expressed as percentages of the corresponding starting rate.

This is a direct physiological measurement from a prepared tissue sample, not direct measurement of electrical neuronal activity, muscle contraction, endurance, reaction time, pain, or consciousness. A lower measured oxygen-consumption rate could generate biological questions, but it does not establish the extent of any real-world weakness or disability without separate experiments. It also does not measure the metabolic processing of THC or ethanol in a whole living subject.

Study design and endpoint: the necessary distinctions

How different were glycolytic and oxidative muscles before exposure?

Baseline oxygen consumption was greater in the 12-week-old soleus than in the same-age gastrocnemius: 9.58 ± 0.93 versus 7.07 ± 0.68 µmol O₂/min/g dry weight (reported p < 0.05). The ± values in this paper are standard errors of the mean (SEM), not standard deviations, individual ranges or measurement uncertainty for a legal specimen.

In the 49-week group, the baseline rates were approximately 8.13 ± 0.84 for soleus and 8.07 ± 0.62 for gastrocnemius in those same units. The study reported no difference between those two older muscle types at baseline. Accordingly, the authors investigated a physiologically plausible interaction between muscle metabolic phenotype and age. The experiment does not prove a universal human age-related hierarchy in sensitivity to cannabis or ethanol.

What do the original numerical results show?

For clarity, the following table retains the study’s negative signs, indicating decreases from each preparation’s own starting mitochondrial-respiration value. The figures are reported mean ± SEM at the highest stated exposure, not paired estimates of legal impairment. Statistical interpretations are confined to comparisons that the authors reported.

One especially important comparison is −49.92% for young gastrocnemius versus −27.22% for young soleus under the combined THC/ethanol condition (reported p < 0.05). This supports an experimentally observed muscle-type difference. It does not show that all oxidative muscle is “protected,” nor that skeletal muscle in a person will behave like either prepared sample.

Was the combined effect uniformly stronger than alcohol alone?

No. The young gastrocnemius showed a stronger decrease with the combined solution, but the 49-week gastrocnemius did not show a statistically significant aggravation. The young soleus had a numerically smaller decrease in the combined condition than in the ethanol-alone condition, and the 49-week soleus showed a different pattern again. The experiment does not support a blanket statement that cannabis necessarily increases every alcohol-related muscle effect across all tissues or ages.

Likewise, a statistically nonsignificant comparison is not proof that the conditions are equivalent. With only four and three animals in the respective age groups, uncertainty can be substantial. Dose-step observations from the same fibers also do not provide the independent replication that would be required for a broad patient-level prediction.

Does the experiment establish chemical or pharmacological “synergy”?

It establishes an enhanced combined-condition reduction in one young glycolytic preparation, not a validated general pharmacological synergy model. A formal synergy analysis usually requires a well-defined reference expectation for independent effects, appropriate controls, exposures, model specification, and uncertainty. Here the THC reagent was delivered in ethanol, and the paper estimated a putative THC-only contribution by subtracting the ethanol condition’s effect.

That approach can describe incremental laboratory effects, but it should not be confused with a fully characterized two-drug interaction in living humans. No human concentration-response surface, inhaled THC bioavailability, blood ethanol pharmacokinetic curve or genotype-stratified interaction was measured. The safer formulation is that the combined experimental solution produced a larger respiration decrease in young rat gastrocnemius.

Can these percentages be applied to a blood toxicology result?

No valid direct conversion is available from this study. A laboratory might report ethanol concentration in venous whole blood, serum, plasma or breath, or THC and metabolites in whole blood, oral fluid or urine. Those are analytically distinct measures, with different units, kinetics and interpretive limits. The rat study did not report any such post-administration human drug concentration. Its chamber molarity is not a legal BAC and its percentage loss of oxygen uptake is not a validated impairment percentage.

Even when a blood assay is appropriately validated, the result must be connected to specimen type, collection time, analytical uncertainty, pharmacokinetics and independent behavioral or medical evidence. See the site’s discussion of absorption, distribution, metabolism and elimination for why exposure histories cannot be reconstructed from an unrelated cellular result. A lower mitochondrial rate cannot be used to back-calculate when someone drank or smoked, or to assign the cause of a collision.

What would a scientific expert need before making a human clinical claim?

Evidence of an observed human effect would require a different research design. Investigators would need an appropriate human population, ethically controlled exposure or carefully characterized observational exposure, verified drug measurements and timing, relevant physical-performance outcomes, and transparent treatment of confounding and repeated measurements. For an alleged injury, contemporaneous clinical findings, competing causes and a case-specific temporal record would also matter.

Forensic reports should distinguish mechanistic plausibility from demonstrated injury or impairment. A mitochondrion consuming less oxygen in a permeabilized rat fiber is an objective laboratory measurement. Weakness, fatigue, rhabdomyolysis, gait alteration, crash risk, and subjective intoxication are different endpoints. None was directly measured as a human outcome here. The study likewise provides no validated sensitivity, specificity, diagnostic threshold, or individual error rate for attributing impairment.

What are the main scientific limitations?

The animal denominator is very small: four young male rats and three middle-aged male rats. There were no female animals, no human volunteers and no population-based sample. Tissue was excised and studied outside the body, which prevents direct extrapolation to normal circulation, metabolism, inflammatory response or behavior in an intact organism. The chosen muscles differ in fiber characteristics; neither represents every skeletal muscle.

Repeated fiber runs and concentration steps were used in the analysis. These improve resolution within a preparation but should not be treated as wholly independent biological subjects. The reported ± values are SEM, and nominal p values do not eliminate design limitations or justify individual predictions. The additive subtraction used to estimate a separate THC contribution is another analytical assumption, not an independently observed THC-only outcome. Finally, the authors’ mechanistic interpretation should not be expanded into a claim about human blood THC, alcohol elimination, driving impairment or medical causation.

How should the study be cited and described in an expert report?

A scientifically restrained description would identify the animal species, ex vivo skeletal-fiber preparation, actual n, treatment concentrations, comparator vehicle, mitochondrial oxygen-consumption endpoint and the specific age/muscle subgroup showing an incremental combined-condition effect. It should also state which other comparisons were nonsignificant and that no individual human impairment or injury endpoint was assessed.

For real evidence, the first questions remain what specimen was taken, what analyte was measured, by what method and with what validated limitations. Confirmatory drug testing may establish chemical identity or concentration when methodologically appropriate; it still cannot, by itself, convert a rat muscle-oxygen experiment into a person’s behavior or a legally dispositive cause.

Frequently asked questions

Did the scientists give alcohol and marijuana to seven living rats?

No. They removed gastrocnemius and soleus muscle tissue from seven rats and exposed prepared muscle fibers to ethanol or THC dissolved in ethanol inside an oxygen-measurement chamber. The exposures were not human-equivalent drinks or smoked-cannabis doses.

Did THC always make ethanol’s mitochondrial effect worse?

No. A larger decrease with the combined solution was reported in 12-week gastrocnemius. The same aggravation was not established in 49-week gastrocnemius, and soleus showed different responses. “Always” exceeds the study.

Does a 49.92% drop mean a driver loses half of their muscle strength?

No. The percentage is the change in oxygen consumption in prepared rat muscle fibers relative to their own baseline. The investigators did not measure human strength, coordination or driving.

Was blood alcohol concentration or blood THC measured?

No human or rat post-exposure BAC or whole-blood THC series was reported. The treatment figures are laboratory solution concentrations in mol/L. They cannot be substituted for venous whole-blood, serum, breath or oral-fluid analytical results.

Did the study independently quantify a pure THC-only effect?

The THC preparation used ethanol as its solvent. The authors compared the combined solution with ethanol alone and estimated a THC contribution by mathematical subtraction. This should not be presented as a separately measured ethanol-free THC treatment response.

What was the difference between the two muscles?

Gastrocnemius is comparatively glycolytic and soleus comparatively oxidative. Young soleus had higher baseline respiration, and the combined THC/ethanol condition produced a smaller mean decrease in young soleus than young gastrocnemius. This tissue-dependent effect is not a universal clinical protection rule.

Could this paper establish that THC and alcohol caused a particular person’s injury?

No. Causation in an individual requires relevant patient or incident evidence and a method suited to that question. This mechanistic animal-fiber experiment supplies neither a validated human effect threshold nor an event-specific causal test.

Primary scientific source

Charles A-L, Giannini M, Meyer A, Charloux A, Talha S, Vogel T, Raul J-S, Wolff V, Geny B. Cannabis (THC) Aggravates the Deleterious Effects of Alcohol (EtOH) on Skeletal Muscles’ Mitochondrial Respiration: Modulation by Age and Metabolic Phenotypes. Biology. 2024;13(12):1080. doi:10.3390/biology13121080. The discussion here concerns the reported original experimental design and findings, not a diagnosis or assessment of any individual case.

Educational scientific analysis prepared for the Forensic Toxicology Working Group Members. Interpretation of a specific laboratory result or incident requires the actual records, validated methods, and independent case evidence.