Cannabis use and its relationship with mobilization efficiency, hematological recovery and neurologic response after hematopoietic stem cell transplantation in patients with multiple sclerosis: A single center, eight-year experience

Imagine your body is a bustling city, and inside it lives a tiny, elite rescue squad called the immune system. Sometimes, in a condition called Multiple Sclerosis (MS), this squad gets confused and starts attacking the city's own roads and bridges (the nerves). To fix this, doctors sometimes use a "hard reset" called a stem cell transplant. Think of this as evacuating the confused rescue squad, giving the city a break, and then sending in a brand-new, fresh team to rebuild. But before the new team can move in, doctors have to go out and find them, a process called "mobilization," where they call the cells out of their hiding spots in the bone marrow.

Now, here is where things get interesting: many people with MS use cannabis (marijuana) to help with pain or muscle stiffness. But doctors have been wondering: does this plant stuff mess up the rescue mission? Does it make it harder to find the new cells? Does it slow down the rebuilding? Or, could it actually be a secret helper? This study dives into that exact question, looking at whether using cannabis changes how well the transplant works, how fast the blood cells recover, and how well the patients feel afterward.

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The Great Stem Cell Hunt: A Story of Marijuana and MS

In a clinic in Puebla, Mexico, a team of researchers decided to play detective. They looked back at 184 adults with Multiple Sclerosis who had undergone a "hard reset" transplant between 2018 and 2025. They wanted to see if the patients' history with cannabis changed the outcome of the big medical event. To solve the mystery, they split the patients into three groups:

1. The Active Smokers: 16 people who were still using cannabis during the transplant process.
2. The Ex-Smokers: 76 people who used to smoke but had stopped at least a year before the transplant.
3. The Non-Smokers: 92 people who had never touched cannabis, matched perfectly to the other groups by age, weight, and how sick they were before the surgery.

The scientists checked three main things:

• The Mobilization: How many "rescue cells" (CD34⁺ cells) could they pull out of the patients?
• The Recovery: How fast did the blood counts (white blood cells, platelets, etc.) bounce back after the transplant?
• The Neurology: Did the patients get worse, stay the same, or get better? They measured this using a score called EDSS, which tracks how much a person's disability affects their daily life.

The Big Surprise: The "Ex-Smoker" Boost

The results were a bit like finding a hidden bonus level in a video game. When the researchers looked at the Ex-Smokers, they found something cool: these patients had higher numbers of mobilized stem cells compared to the Non-Smokers.

In the raw numbers, the Ex-Smokers had a median of 681.0 ×10⁶/kg of cells, while the Non-Smokers only had 439.0 ×10⁶/kg. That's a big difference! Even when the scientists used complex math to account for age, weight, and the specific type of MS the patients had, the Ex-Smokers still showed a positive trend, suggesting that having used cannabis in the past might actually help the body release more of these helpful cells.

However, there was a catch. The Active Smokers (the 16 people smoking during the procedure) didn't get this bonus. Their cell counts were high, but they weren't significantly different from the Non-Smokers. It seems like the "magic" of cannabis for mobilization might only happen if you've used it before and then stopped, rather than if you are using it right at the moment of the transplant.

The Recovery Race: No Delays

Next, the team checked the recovery race. After the transplant, the body has to rebuild its blood supply from scratch. The researchers worried that cannabis might slow this down, like a traffic jam on the highway.

But guess what? No traffic jams found.

• White Blood Cells: The Ex-Smokers actually recovered slightly faster (median 8 days) compared to Non-Smokers (median 9 days).
• Neutrophils, Lymphocytes, and Platelets: Everyone recovered at about the same speed (around 8 days for everyone).

The paper suggests that having used cannabis in the past does not hurt the body's ability to rebuild its blood. In fact, it might even give the white blood cells a tiny head start.

The Brain Score: A Shield Against Worsening

The most exciting part of the story involves the patients' brains and nerves. The researchers tracked the EDSS score (the disability score) at 3, 6, and 12 months after the transplant.

At first glance, the average scores looked the same for everyone. But when they looked at who got worse, a pattern emerged. The Ex-Smokers were much less likely to see their condition decline in the short term.

• At 6 months, only 4.4% of the Ex-Smokers got worse.
• In contrast, 18.6% of the Non-Smokers got worse.

Even after the scientists adjusted for everything else (like how sick the patient was to begin with, their age, or their gender), the data suggested that being an Ex-Smoker was a protective factor. The math showed that Ex-Smokers had an adjusted odds ratio of 0.21 for getting worse at 6 months. In plain English, this means they were significantly less likely to experience a setback compared to those who never used cannabis.

What Does This All Mean?

The researchers are careful to say they haven't "solved" the puzzle yet. They don't know why the Ex-Smokers did better. Maybe the cannabis changed the environment in the bone marrow, or maybe it tweaked the body's immune system in a way that helped the transplant stick. They also note that the study was done at just one clinic and looked back at old records, so they need bigger, forward-looking studies to be 100% sure.

But here is the takeaway: If you have used cannabis in the past, it doesn't seem to ruin your transplant. In fact, this study suggests it might help you gather more stem cells and keep your disability from getting worse in the first year after the surgery. And if you are smoking during the transplant? Well, that didn't seem to give you the extra boost, but it didn't hurt you either.

So, for the curious teenager reading this: The body is a complex machine, and sometimes the things we think might break it actually help it run smoother. This study suggests that for MS patients getting a stem cell transplant, a history of cannabis use might be a secret ally in the fight for recovery.