Disease-modifying therapies (DMTs) can be effective treatment for multiple sclerosis (MS). These drugs are approved by the U.S. Food and Drug Administration (FDA) because of their proven ability to slow disease progress in people with MS. But for people with relapsing MS, it’s common to switch DMTs over the course of the disease.

In a large study spanning around 20 years, researchers followed 110,326 people diagnosed with relapsing-remitting MS (RRMS). The study found that participants switched DMTs 159,309 times within six months of starting a new drug.

There are several reasons you and your neurologist may decide to switch your MS treatment from one DMT to another, including bothersome side effects and continued MS relapses (also known as flares) and disease progression. Additionally, medications sometimes become less effective over time.

How DMTs Work

MS is an autoimmune disease in which the immune system mistakenly attacks the myelin sheath that covers nerves. DMTs don’t treat MS symptoms, but they work by blocking parts of the immune system that damage the central nervous system (CNS, or brain and spinal cord). Research shows that early and continued use of DMTs for MS can reduce the rate of MS flares, lessen inflammation in the CNS, and delay disability progression.

More than 25 DMTs have been approved by the FDA for the treatment of MS, and more new DMTs are in development. Some DMTs are taken orally, and others are taken by subcutaneous (under the skin) injection or by intravenous (IV) infusion. Injected drugs can either be self-injected at home or given in a clinical setting. Infused drugs must be administered by a health care provider.

A few of the DMTs approved to treat MS include:

• Dimethyl fumarate (Tecfidera)
• Fingolimod (Gilenya)
• Glatiramer acetate (Copaxone, Glatopa)
• Interferon beta 1a (Avonex)
• Natalizumab (Tysabri)
• Ocrelizumab (Ocrevus)
• Ofatumumab (Kesimpta)

If switching disease-modifying treatments is appropriate for you, your neurologist will provide detailed information about different DMTs, potential side effects, and how they are taken. That way, you can make an informed decision based on your treatment goals and preferences.

Read more about specific medications in this list of treatments for multiple sclerosis.

Why Do DMTs for MS Sometimes Stop Working?

According to neurology research, one reason DMTs stop working effectively is that a person’s body may eventually develop antibodies (immune proteins) against these drugs. Normally, your immune system produces antibodies to fight foreign invaders such as bacteria and viruses.

When you take MS medication, your immune system may gradually recognize the drug as a foreign substance and make antibodies against it, preventing it from working properly. People taking interferons or alemtuzumab (Lemtrada) have a higher risk of developing these types of antibodies.

Allowing Time for a DMT To Take Effect

Before considering a treatment switch, doctors usually wait until enough time has passed to allow a DMT to fully take effect — on average, at least one year. That’s usually long enough to monitor the response to a new treatment with magnetic resonance imaging (MRI) and watch for worsening symptoms. It’s important to maintain your treatment plan and continue taking your current medication exactly as directed to make sure it works as effectively as possible.

Signs It May Be Time To Consider Switching DMTs

Neurologists treating MS will look for signs that indicate it may be advisable to consider switching DMTs, including one of the following reasons.

1. Increase in MS Relapses and Symptoms

Despite following your DMT treatment plan as directed, you may still experience signs of breakthrough disease, including:

• Increased relapses in the case of RRMS or clinically isolated syndrome (CIS) or more symptoms in active secondary-progressive MS (SPMS)
• Continued disease activity (persistent or worsening symptoms)
• New or worsening brain lesions on MRI scans

Any of these factors may be signs it’s time to consider different treatment options.

2. Increased Risk of Serious Side Effects

Because DMTs suppress the immune system, they increase the risk of infections. For some people, that may be a reason to discontinue a particular medication. The good news is that DMTs are becoming safer, and the incidence of infections is lower with newer DMTs.

Progressive Multifocal Leukoencephalopathy

Progressive multifocal leukoencephalopathy (PML) is a rare, but serious, brain infection associated with some DMTs. PML can cause disability or even death. PML is very uncommon, even among people taking DMTs, but all FDA-approved MS treatments still include a black box warning about the risk. If you are taking a DMT, your doctor will monitor you for infections, including PML.

3. Disease Progression

If a relapsing form of MS advances to progressive MS, it may be time to switch medications. Neurologists track disease progression and measure the effectiveness of DMTs with tools such as the Expanded Disability Status Scale (EDSS) and assessments of quality of life in comparison to your baseline (original) symptoms.

Your doctor may recommend tests such as MRI scans of the CNS to look for enlarging or new lesions. MS activity that’s visible on MRI scans usually indicates MS disease progression.

Transition to Secondary Progressive MS

Most people with MS are initially diagnosed with relapsing multiple sclerosis, which is characterized by symptom flare-ups followed by periods of relative recovery. People with RRMS often progress to SPMS, in which symptoms and disability gradually worsen. Progression to SPMS early in your disease course can be a sign that your current treatment may not be effective.

Shared Decision-Making and Switching DMTs

Making treatment decisions can be stressful, but open communication can help ensure you meet your treatment goals. Through shared decision-making, your doctor’s recommendations and your concerns are discussed in detail in order to find a treatment option that best fits your lifestyle and needs. Shared decision-making has been shown to improve the health outcomes of people living with MS.

Make sure you regularly follow up with your neurologist and attend any scheduled appointments. Your doctors need to see how your MS is progressing in order to determine if your current DMT is working effectively.

No one knows your MS symptoms better than you. Always let your health care providers know about any new or worsening symptoms.

If you’re considering switching MS treatments, read about washout periods — time between stopping one treatment and beginning another — and when they may be needed.

Talk With Others Who Understand

MyMSTeam is the social network for people with multiple sclerosis and their loved ones. On MyMSTeam, more than 211,000 members come together to ask questions, give advice, and share their stories with others who understand life with MS.

Do you have questions about switching medications for MS? Have you and your doctor discussed a treatment change? Share your questions and experiences in the comments below, or start a conversation on your Activities page.