Changing treatments is common for people with multiple sclerosis (MS). Many switch disease-modifying therapies (DMTs) at least once — and often more — as they search for what works best. You might think about switching DMTs for a few reasons. Maybe side effects from your current DMT are hurting your quality of life, or perhaps you’re still having relapses even after several months on the medication.

If you’re thinking about switching treatments, your healthcare provider may recommend a washout period beforehand.

What Does ‘Drug Washout’ Mean?

A drug washout is the time between stopping one medication and starting another. The break allows the first drug to clear from your system so it doesn’t interfere with the effects of the new one.

Keep reading to learn eight key facts to consider when planning a washout period between MS DMTs.

1. Washout Periods for MS DMTs Are Common

If you’re living with MS, you’ll likely consider changing medications at some point. In a study of more than 110,000 people with MS who, altogether, tried nearly 270,000 DMTs, researchers found that about 68 percent stopped a new treatment within two years of starting it.

You might stop taking a DMT if:

• It’s not controlling your MS well enough.
• Your disability gets worse while on the drug.
• You keep having MS relapses.
• Side effects are too difficult to manage.
• You’re allergic to the drug.
• It’s hard to follow the medication schedule.
• Your immune system develops resistance or neutralizing antibodies to the drug.
• It’s too expensive.
• You don’t need the medication (such as being age 55 or 60 with long-term disease stability and no signs of acute disease).

In these situations, you and your doctor may decide to stop your current DMT, go through a washout period, and try a different one.

2. DMT Washout Periods May Help Prevent Side Effects and Increase Tolerability

DMTs can be effective in the treatment of multiple sclerosis, but some — especially highly effective DMTs — may come with a high risk of side effects. A washout period helps reduce the risk of overlapping side effects from two medications.

Some DMTs stay in your system for a little while, so starting a new one too soon could mean both medications are active in your body at the same time. This overlap may increase the chance of side effects or drug interactions.

3. DMT Washout Periods Might Raise the Risk of Flares

A major downside of a washout period is that your MS may become harder to control. Without ongoing treatment, you may experience a flare or relapse (a period of new or worsening symptoms). For people with relapsing forms of MS, including relapsing-remitting MS (RRMS), clinically isolated syndrome, and active secondary progressive MS, flares are caused by inflammation in the central nervous system (the brain and spinal cord).

During a washout period, your doctor may recommend regular follow-up testing to look for early signs of a flare. This might include blood tests to check your levels of lymphocytes (white blood cells) or magnetic resonance imaging (MRI) scans to look for new lesions (areas of damage in your nervous system) compared to your baseline before stopping treatment.

If you do have a flare during a washout period, your doctor may recommend short-term treatment with high-dose corticosteroids to help ease your MS symptoms until your new DMT takes effect. Corticosteroids can be taken as pills (oral route) or by injection (intravenous route).

Once you start taking a new DMT, keep in mind that it can take three to six months to become fully effective.

4. Different DMTs Require Different Washout Periods

In many cases, there’s limited research on just how long a washout period should be. However, MS experts have shared general guidelines for different DMTs based on how these medications affect the body:

• Alemtuzumab (Lemtrada) and cladribine (Mavenclad) — The washout period lasts until lab tests show no signs of active disease.
• Dimethyl fumarate (Tecfidera) — No washout period is needed unless you have lymphopenia (low lymphocyte levels).
• Fingolimod (Gilenya, Tascenso ODT) and siponimod (Mayzent) — A few weeks may be needed if you have low lymphocyte levels.
• Glatiramer acetate (Copaxone, Glatopa), rituximab (Rituxan), or interferons — Usually, no washout period is needed.
• Mitoxantrone — Washout period lasts three to six months.
• Natalizumab (Tysabri) — Washout period lasts up to 12 weeks.
• Ocrelizumab (Ocrevus) — Washout period lasts up to three months.

The length of a washout period may differ depending on the DMTs you're switching from and to and your personal health details.

For medications that work by binding to the cell receptor CD20, such as ofatumumab (Kesimpta), some doctors skip a washout period to avoid a flare-up. However, if you’re switching due to an infection or low immune proteins, a short break may still be needed. Starting the new treatment quickly can help prevent MS from becoming more active.

Medications like teriflunomide (Aubagio) can take up to two years to leave the body. However, your doctor may speed up the process with a rapid elimination protocol. In this detailed medical plan, medications such as cholestyramine or activated charcoal are taken for 11 days. The protocol may be used for people who have severe side effects or are planning to become pregnant.

Your doctor may recommend a longer or shorter washout period depending on your health needs and their experience and knowledge about a specific DMT.

5. DMT Washout Periods Can Vary From Person to Person

Several other factors can affect the length of a washout period. When deciding on the right timeline, your doctor may consider:

• How active your MS is
• What other health conditions you have
• Why you’re switching treatments

Work with your doctor to weigh the risks and benefits of different options. They know your history and priorities and can guide you in choosing the safest approach.

6. Your Doctor May Suggest Tapering the DMT

Most of the research, clinical trial results, and treatment guidelines assume that people will stop a DMT all at once. However, your doctor may recommend tapering — slowly lowering the dose before stopping.

One study of people with MS taking natalizumab found that tapering reduced the risk of MS flares. Some researchers also suggest tapering fingolimod to help avoid rebound flares. However, tapering before a washout period hasn’t been studied for most DMTs, so it’s unclear whether this strategy lowers or raises relapse rates.

Your doctor can advise you on whether it’s better to stop your current DMT all at once or taper gradually.

7. Other Situations May Require Washout Periods

You may need a washout period if you’re planning to become pregnant. Your decision will depend on your disease progression and overall health. Ideally, people with MS should have stable disease for six to 12 months before trying to conceive.

Clinical trials for DMTs haven’t included pregnant or lactating women, according to the journal Neurology Clinical Practice, so there’s little research on the safety of DMTs during pregnancy. Currently, no MS DMTs are approved by the U.S. Food and Drug Administration (FDA) for use while pregnant or breastfeeding. That’s why doctors usually recommend a washout period before trying to conceive.

Washout recommendations vary by medication:

• Alemtuzumab — Avoid pregnancy for four months after stopping.
• Dimethyl fumarate — Wait at least one week.
• Fingolimod — Wait at least two months due to risk of harm to the baby.
• Glatiramer acetate — No washout period is needed, and this drug may be used during pregnancy.
• Interferon-beta — This medication may be used throughout pregnancy, but some doctors suggest a two-week washout.
• Natalizumab — Wait two to three months.
• Ocrelizumab and ofatumumab — Wait one to three months.
• Teriflunomide — Stop two to four months before you plan to get pregnant. A rapid elimination protocol is recommended.

Your doctor may also suggest a washout period if you need treatment for another health condition. Talk with your neurologist if you’re not sure about discontinuation of your DMT.

8. Don’t Change Your Medication Without Talking to Your Doctor

Always take your DMTs as prescribed. Skipping doses, stopping early, or changing how you take it can make your MS worse.

If you’re having problems with your current treatment, talk to your neurology care team. There are many DMTs for MS, and your neurologist can help you find a treatment option that better fits your needs. They can also guide you through a safe washout period to reduce the risk of flares.

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