Clemastine for Multiple Sclerosis: Summarizing the Research on This Antihistamine’s Potential Use

There’s no cure for multiple sclerosis (MS). But treatments to lessen its symptoms and slow down its progression have come a long way over the years. And studies continue to search for new treatments.

One medication that’s sparked interest for treating MS is clemastine, an antihistamine. It’s shown promise in some studies. But the data supporting its effectiveness for MS are conflicting.

Learn more about how clemastine may work to treat MS and its side effects.

Promotion disclosure

Clemastine

Avg retail price

$1253.56(Save 97.22%)

GoodRx discount

$34.79

Compare all prices

What is clemastine normally used to treat?

Clemastine is a first-generation antihistamine. It works by blocking a natural substance in the body called histamine. The body releases histamine in response to an allergen (a substance that may cause an allergic reaction). Another first-generation antihistamine you’ve probably heard of is the over-the-counter (OTC) medication diphenhydramine (Benadryl).

Like diphenhydramine, clemastine is normally used for short-term allergy relief. It helps relieve symptoms such as runny nose, watery eyes, and sneezing. Clemastine can also be used to relieve itchiness from chronic hives or angioedema.

Clemastine is currently only available in the U.S. as a prescription medication. It's no longer available OTC.

How does clemastine work for multiple sclerosis?

In MS, the immune system mistakenly attacks the brain and spinal cord. This process can damage myelin. Myelin is a fatty substance that coats the nerve fibers of the central nervous system.

When myelin is damaged, nerve signaling throughout the body can significantly slow down or become blocked. This contributes to the symptoms of MS, such as difficulty walking and vision changes.

Clemastine is thought to treat MS by repairing damaged myelin, which would improve nerve signaling. But clemastine isn’t FDA approved to treat MS. So its use for this is considered off-label.

EXPERT PICKS: WHAT TO READ NEXT

• A unique perspective: Read advice on managing MS from a person living with the condition.

• Injectable MS treatments: Explore FDA-approved injections and infusions that can treat multiple sclerosis.

• Oral MS medications: Discover the MS medications that can be taken by mouth.

Clemastine and MS research findings

We currently don’t know how clemastine helps treat MS. The study results so far have had differing results.

A small clinical trial in 2017 (called the ReBUILD trial) first studied clemastine for MS. All participants in this 5-month study had relapsing MS. They either took clemastine 5.36 mg by mouth twice a day or a placebo pill. All participants were also stable on a disease-modifying therapy (DMT) for MS. DMT are medications that help prevent relapses and slow the progression of MS.

This study found that clemastine helped improve how quickly nerve signals traveled from the eye to the brain. That finding suggests that it may improve vision. Researchers from this study also concluded that clemastine may help repair myelin.

After researchers published these study results, clemastine became a possible treatment to consider for MS. So more research began.

Does clemastine reverse or worsen MS?

This is an ongoing question. 

Unlike the ReBUILD trial above, a 2024 study called the TRAP-MS trial actually found that clemastine may worsen MS. In this study, participants with MS took clemastine 8 mg daily, split over 3 doses. Unfortunately, three participants in this study had worsening disability and disease progression at a faster rate compared to when they started the study. Some blood tests also showed higher inflammation levels. 

Only a small number of patients received clemastine in this study. But the clemastine portion of this study was stopped early due to these results.

Since clemastine study results have been mixed, more research needs to be done to determine if it’s actually helpful or harmful for MS. Before taking clemastine for MS, speak with a healthcare professional about whether or not it may be right for you.

What are the known clemastine side effects when used for MS?

Clemastine’s side effects in MS haven’t been widely studied. The ReBUILD trial, mentioned above, reported that clemastine’s main side effect was fatigue. But there are some others to be aware of.

We know more about clemastine’s side effects when it’s used to treat allergy symptoms. We expect many of them to be the same if it’s used to treat MS. Some of them may be even more noticeable because the doses seen in MS studies are higher than the dose used to treat allergies.

Common known side effects of clemastine include:

• Sleepiness

• Fatigue

• Dizziness

• Headache

• Dry mouth, nose, or throat

• Blurry vision

• Confusion

• Loss of coordination

Since clemastine can make you sleepy and dizzy, it's best to avoid driving until you know how the medication affects you. This is especially true for adults over age 60. Also, steer clear of alcohol or other medications that can make you drowsy while taking clemastine; combining them raises the risk of excessive sleepiness.

Can you combine clemastine with other MS medications?

Most likely. Participants in the ReBUILD trial were receiving a DMT for MS while they took clemastine. This includes medications such as interferon beta-1b (Betaseron), interferon beta-1a (Avonex), and glatiramer (Copaxone). Teriflunomide (Aubagio), ublituximab (Briumvi), and dimethyl fumarate (Tecfidera), are also possible DMTs, among others. In the study, participants took clemastine in combination with these DMTs and didn’t report any problematic side effects.

Still, taking clemastine with other MS medications hasn't been well studied. Let your healthcare professional know if you’re thinking about taking clemastine in combination with other medications. They can let you know if doing so is a safe option for you.

Was clemastine fumarate discontinued?

You may recall seeing clemastine on the shelves of your local pharmacy. That’s because clemastine used to be available as an OTC tablet that contained 1.34 mg of clemastine. OTC clemastine is now discontinued in the U.S.

Clemastine is currently only available as a prescription medication. It's available as an oral tablet that contains 2.68 mg of clemastine and an oral syrup that contains 0.5 mg of clemastine per 5 mL liquid.

Why trust our experts?

Written by:

Sonja Jacobsen, PharmD, BCPS, BCOP

Sonja Jacobsen, PharmD, BCPS, BCOP,  is a clinical oncology pharmacy specialist currently practicing in Seattle. She has been practicing as a pharmacist since 2015 and is licensed to practice in Washington state and North Carolina.

Edited by:

Joshua Murdock, PharmD, BCBBS

Joshua Murdock, PharmD, BCBBS, is a licensed pharmacist in Arizona, Colorado, and Rhode Island. He has worked in the pharmacy industry for more than 10 years and currently serves as a pharmacy editor for GoodRx.

Reviewed by:

Bailey E. Eason, PharmD, MS, BCPS

Bailey Eason has been licensed for 6 years and has held licenses in three states (North Carolina, Virginia, and Illinois). She has held positions as a health-system pharmacy administration resident, operating room pharmacy manager, pharmacy manager of clinical operations: surgery, neurology and controlled substances, and most recently as program director  of drug diversion for a large academic health system.

Our editorial standards

Meet our experts