Marijuana has long been known for its mind-altering effects, but its impact on the body—particularly on motor control—has been less understood.
While some users report difficulty speaking, swallowing, or even breathing after consuming cannabis, others—particularly those with neurodegenerative diseases like multiple sclerosis (MS)—swear by its benefits.
So, what’s really happening inside the brain and body when someone uses marijuana?
A new study, published in Neuropharmacology by researchers from the University of Cadiz in Spain, has uncovered how marijuana directly affects the motor neurons that control muscle movement.
The findings suggest that the same mechanism that causes slurred speech or muscle weakness in recreational users may actually help people suffering from conditions that cause muscle hyperactivity.
Led by Bernardo Moreno from the university’s NeuroDegeneration and NeuroRepair Group, the team investigated how psychoactive compounds in marijuana interact with motor neurons.
They found that these compounds inhibit communication between neurons, reducing the strength of muscle contractions.
At first glance, this might sound like a negative side effect.
But here’s where things get interesting—this very process could explain why cannabis helps patients with diseases like MS, ALS, and epilepsy.
The Surprising Way Marijuana Affects Muscle Control
To understand marijuana’s impact on the nervous system, Moreno’s team conducted experiments on lab mice, focusing on the motor neurons that control the tongue—a key muscle for speaking, breathing, and swallowing.
- They introduced synthetic analogues of marijuana’s psychoactive compounds and observed how they affected nerve cells.
- The results were striking: The compounds slowed down the transmission of information between motor neurons, weakening muscle contractions.
- In simple terms, marijuana made it harder for the neurons to “tell” muscles what to do.
Moreno explains:
“The motor neuron—that is, the one that gives the order to the muscle to contract—sees its activity reduced, which, as a consequence, would weaken the strength of the muscle contraction.”
This explains why some marijuana users experience temporary difficulty speaking or swallowing after using the drug.
But in the context of neurodegenerative diseases, this effect could actually be a benefit rather than a drawback.
When Muscle Weakness Is a Good Thing
Most of us assume that weakening muscle contractions is bad—but that’s not always the case.
For people with multiple sclerosis (MS), amyotrophic lateral sclerosis (ALS), or epilepsy, muscular hyperactivity—or excessive, uncontrollable muscle contractions—can cause pain, spasms, and difficulty controlling movement.
This is where marijuana’s effects take on a different role.
Moreno’s team suggests that cannabis-induced suppression of motor neuron activity may actually help relieve symptoms in people suffering from these conditions.
Here’s why:
- In MS patients, muscles often contract involuntarily due to misfiring signals from damaged nerves. By dampening motor neuron activity, marijuana may help reduce these spasms.
- In ALS, the disease causes neurons to send uncontrolled signals, leading to muscle rigidity and cramping. Marijuana’s ability to slow down these signals could bring relief.
- For epilepsy patients, seizures are often linked to overactive neural activity. Marijuana’s calming effect on neurons may help control these episodes.
This suggests that what might be an “undesirable” side effect for healthy users—such as difficulty speaking—could actually be therapeutic for those with neurological disorders.
Marijuana’s Impact on the Brain: More Than Just Motor Neurons
This isn’t the only study to shed light on how cannabis interacts with the nervous system.
A separate study from last year explored how long-term marijuana use affects brain connectivity.
The research found that:
- Heavy marijuana users tend to have a smaller orbitofrontal cortex—a region of the brain involved in decision-making.
- But their brains compensate for this loss by increasing connectivity in other areas—essentially rewiring themselves to maintain function.
- The effect was most pronounced in users who started young, suggesting that marijuana affects brain plasticity over time.
This raises an important question: Could long-term marijuana use actually reshape neural pathways in a way that helps people with neurodegenerative diseases?
The Bigger Picture: Could Marijuana Be Used as a Targeted Therapy?
While cannabis is still controversial as a medical treatment, research like this could pave the way for more targeted therapies. If scientists can isolate the compounds responsible for reducing motor neuron activity, they could potentially develop new drugs that offer the benefits of marijuana without the psychoactive effects.
Moreno’s study is a step toward understanding the complex relationship between marijuana and the nervous system. It suggests that:
- Marijuana doesn’t just affect mood and cognition—it has a direct impact on motor control.
- The same mechanism that makes speech or movement sluggish in some users could actually help people with neurological conditions.
- Future therapies could harness this effect to develop better treatments for MS, ALS, and epilepsy.
As Moreno himself puts it:
“In pathological processes associated with muscular hyperactivity, the reduction in motor neuron activity induced by cannabis could lead to symptom improvement.”
For now, marijuana remains a double-edged sword—offering both side effects and potential benefits.
But as research continues, we may discover that its impact on the nervous system is more useful than we ever imagined.
Sources:
Neuropharmacology, University of Cadiz, BBC, The Washington Post
