Switching Antidepressants: Cross-Tapering, Washouts and What to Expect

Switching antidepressants is usually done in one of four ways: tapering the old drug and waiting before starting the new one, tapering with only a short gap, stopping one and starting the other the next day, or cross-tapering so that the two overlap for a while. Which method fits depends on the two drugs involved, how long you have taken the first one, and how risky a gap in treatment would be for you.

Two situations have strict rules. Monoamine oxidase inhibitors (MAOIs) need a medication-free interval in both directions, and fluoxetine (Prozac) needs a much longer one because it stays in the body for weeks. During any switch, expect some mix of withdrawal effects from the old drug and start-up side effects from the new one. Plan the switch with your prescriber; do not make it on your own.

When a switch makes sense

A switch is one of several next steps when an antidepressant is not working or cannot be tolerated. NICE, the guideline body for England, lists raising the dose, switching within the same class, switching to a different class, switching to or combining with a psychological therapy, or adding a group exercise program as options after a limited response to medication alone. Adding a second medication is a separate route covered in antidepressant augmentation options.

Timing matters. NICE advises that if depression has not responded at all after 4 weeks at a recognized therapeutic dose, the prescriber should first look at adherence and at personal, social or medical factors that could explain the lack of response. A review in Australian Prescriber puts it similarly: a patient is unlikely to respond if there has been no improvement after three to four weeks on an adequate dose. The same review notes there is no evidence that switching to a different class works better than switching within a class.

Before a switch, a careful prescriber will usually check a few things:

• Whether the dose was adequate and taken consistently.
• Whether the diagnosis still fits; NICE advises reviewing the diagnosis and looking for other conditions when treatment has not worked.
• Whether side effects could be managed without changing drugs.
• Whether you have had two or more medications fail, in which case the reasoning in what a psychiatrist considers after two antidepressants have not worked applies.

The four ways to switch

The Australian Prescriber review describes four techniques, from most cautious to most rapid. Each trades one risk for another: a long gap risks the depression returning, while overlap risks drug interactions.

For most SSRIs, five half-lives works out to about five days; fluoxetine is the exception and can remain significantly active five or more weeks after it is stopped. NICE also notes that a faster taper may be appropriate when the reason for stopping is a switch rather than coming off medication altogether.

Which method your prescriber picks depends on the pair of drugs, your history with withdrawal, and how severe your depression has been. If the illness has been severe, a longer untreated gap may be the bigger danger; if the two drugs interact, overlap may be the bigger one. Comparisons of specific pairs are covered in sertraline vs escitalopram, venlafaxine vs duloxetine and how a first antidepressant is chosen.

Switches with fixed waiting periods: MAOIs and fluoxetine

MAOIs such as phenelzine (Nardil), tranylcypromine (Parnate) and the selegiline patch (Emsam) cannot be combined with most other antidepressants, and their labels set minimum gaps. These are not flexible guidelines; the prescribing information lists the combinations as contraindicated.

The fluoxetine rule exists because of its long-lived active metabolite, norfluoxetine, whose elimination half-life is 4 to 16 days; the Prozac label states that active drug persists in the body for weeks after dosing stops. The tranylcypromine label adds that inhibition of the MAO enzyme may persist for up to 10 days after the drug is stopped, and that high-tyramine foods should be avoided for 2 weeks after stopping. NICE recommends that switching to or from an MAOI happen in specialist care or with specialist advice.

If you have taken fluoxetine or an MAOI in recent weeks, tell every prescriber and pharmacist, including for non-psychiatric prescriptions.

What you may feel during a switch

Three different things can happen during a switch, and they can overlap. Sorting them out is one of the main jobs of follow-up visits.

FDA labels for SSRIs list the reported discontinuation reactions, particularly after abrupt stopping: nausea, sweating, low or irritable mood, agitation, dizziness, sensory disturbances such as electric-shock sensations, tremor, anxiety, confusion, headache, lethargy, insomnia, tinnitus and seizures. Some drugs are more likely to cause them. NICE singles out paroxetine and venlafaxine, and the Australian Prescriber review describes venlafaxine as associated with the most severe withdrawal effects and fluoxetine as rarely causing them.

Withdrawal symptoms are not, by themselves, a sign that you have relapsed. NICE advises reassuring people that the symptoms are common and are not a relapse, and that if they are severe the prescriber may restart the original drug at the previous dose and then reduce more slowly. That decision belongs to the prescriber; restarting or adjusting a dose yourself can create its own problems. The site's guide to tapering psychiatric medications safely covers withdrawal in more depth.

Serotonin syndrome: the reason overlap is handled carefully

When two serotonergic drugs overlap, or when a washout is too short, serotonin levels can rise to a dangerous degree. FDA labels describe serotonin syndrome as including:

• Mental status changes, such as agitation, hallucinations, delirium and coma.
• Autonomic instability, such as a fast heart rate, unstable blood pressure, dizziness, heavy sweating, flushing and high body temperature.
• Neuromuscular signs, such as tremor, rigidity, muscle jerks, overactive reflexes and poor coordination.
• Seizures, and gastrointestinal symptoms such as nausea, vomiting and diarrhea.

The Prozac label tells patients to seek medical care immediately if these symptoms occur. Mild nausea or jitteriness early in a new drug does not by itself mean serotonin syndrome. High fever, rigid muscles, confusion or a racing heart during a switch need immediate medical care, such as an emergency room, not a wait for your next appointment.

Interaction risk is not limited to antidepressants. The sertraline label lists linezolid and intravenous methylene blue alongside MAOIs as contraindicated combinations, and many other medications add serotonergic load. Give your prescriber a complete list, including supplements; the checklist in how to prepare your medication history helps.

How long until you know the new drug is working

A switch resets the clock. The new medication needs time at an adequate dose before anyone can judge it, and NICE uses 4 weeks at a recognized therapeutic dose as the point to reassess a complete lack of response. If the new drug is started low and raised gradually, that clock starts once the dose reaches a therapeutic level, not on the first day.

Fluoxetine is slow in both directions. Its label notes that steady-state levels after prolonged dosing take about 4 to 5 weeks to reach, and that dose changes are not fully reflected in blood levels for several weeks. Your prescriber may judge a switch onto or off fluoxetine on a longer timeline than one between two short half-life drugs.

Keeping a simple daily log of mood, sleep, energy and any physical symptoms helps your prescriber tell withdrawal, side effects and slow improvement apart. Structured scores, explained in PHQ-9 and GAD-7 scores explained, make the comparison more objective.

Safety during the switch

Any period of changing doses deserves closer watching. The FDA boxed warning on antidepressants such as sertraline states that antidepressants increased suicidal thoughts and behavior in children and young adults in short-term studies, and the sertraline Medication Guide names people 24 and younger, especially in the first months and when the dose is changed. NICE recommends a review 1 week after starting a new antidepressant for people aged 18 to 25 or anyone with a particular concern about suicide risk.

Agree in advance on how to reach your prescriber between visits and what counts as a reason to call. Tell someone you trust that you are changing medications. If you are thinking about suicide or are in crisis, call or text 988 (the 988 Suicide & Crisis Lifeline) or go to the nearest emergency room. A written plan, described in safety planning for suicidal thoughts, is useful during any medication change.

Common mistakes that make a switch harder

Most problems during a switch come from small gaps in communication rather than from the drugs themselves. These are the ones worth avoiding:

• Stopping the old medication early because the new prescription has arrived. Follow the written schedule, even if it means taking both for a while during a cross-taper.
• Missing doses of a short half-life drug during the taper. Missed or partial doses can bring on withdrawal symptoms, as NICE warns.
• Adding a supplement, over-the-counter product or new prescription without asking. The sertraline label lists St. John's wort, tryptophan, triptans, tramadol and other opioids, lithium, buspirone and amphetamines among the serotonergic drugs that raise serotonin syndrome risk when combined.
• Judging the new drug too soon. A rough first week often reflects the taper, not the new medication.
• Not telling other clinicians. A dentist, urgent care doctor or specialist who prescribes a pain medication or migraine drug needs to know you are mid-switch.
• Using leftover pills from an earlier prescription to "bridge" a gap. Doses and timing should come from the prescriber who is managing the switch.

Questions to ask your prescriber before switching

1. Why switch rather than raise the dose or add something?
2. Which method will we use (washout, short gap, direct or cross-taper), and why for these two drugs?
3. Is there a required waiting period, such as after fluoxetine or an MAOI?
4. Which symptoms are expected withdrawal, and which mean I should call?
5. When will we check in, and how do I reach you between visits?
6. When will we judge whether the new drug is working?
7. Do any of my other medications or supplements interact with the new drug?

Bring the written schedule home, with the date of each dose change. If something feels wrong mid-switch, call rather than guessing. For a broader look at when a regimen needs rethinking, see signs you need a new psychiatric medication plan.

How Dr. Lewis's team approaches medication changes

Ongoing care at the practice includes psychiatric evaluation and medication management, alongside psychotherapy, coaching, lab testing, and nutrition and lifestyle psychiatry. The team includes psychiatrists, psychiatric nurse practitioners, psychotherapists and a health and wellness coach. If you are weighing a switch, a free discovery call is the first step to learn about care options and scheduling. More about the practice's approach is on the medication management page, and the wider set of decision guides is in the choosing psychiatric care guide.

Frequently asked questions

Can I just stop my old antidepressant and start the new one the next day?

Sometimes a prescriber does exactly that, but only for certain pairs of drugs, such as two short-acting SSRIs. For other pairs, especially fluoxetine or MAOIs, a direct switch can cause withdrawal symptoms or a dangerous interaction. Ask your prescriber which method fits your two medications.

Is it normal to feel worse for a week or two after switching?

It can be. Withdrawal effects from the old drug and start-up side effects from the new one often overlap in the first weeks. Feeling dizzy or irritable is different from feeling hopeless, though. Report any worsening mood or thoughts of self-harm right away rather than waiting it out.

Why does fluoxetine need such a long washout before an MAOI?

Fluoxetine and its active metabolite norfluoxetine leave the body slowly, so the drug is still active for weeks after the last dose. The Prozac label therefore requires 5 weeks before starting an MAOI.

Will my new antidepressant work better if it is from a different class?

Not necessarily. A review in Australian Prescriber found no evidence that switching between classes works better than switching within one. The choice usually rests on side effects, interactions and your history.

Can genetic testing tell me which antidepressant to switch to?

Pharmacogenomic tests can flag how you may metabolize certain drugs, but they cannot tell you which drug will work for you. See the guide to pharmacogenomic testing and its limits.

Should my primary care doctor or a psychiatrist handle the switch?

Many uncomplicated switches are handled in primary care. A psychiatrist is more useful after several failed trials, for MAOIs, or when bipolar disorder or other diagnoses are in question. See psychiatrist vs primary care for antidepressants.

Sources

1. Depression in adults: treatment and management (NG222), Recommendations. National Institute for Health and Care Excellence, 2022. nice.org.uk
2. Switching and stopping antidepressants. Australian Prescriber 39(3):76-83 (Keks N, Hope J, Keogh S), 2016. australianprescriber.tg.org.au
3. Prozac (fluoxetine) capsules prescribing information. Eli Lilly and Company (Dista) / DailyMed (NLM), 2026. dailymed.nlm.nih.gov
4. Zoloft (sertraline) prescribing information and Medication Guide. Viatris Specialty / DailyMed (NLM), 2025. dailymed.nlm.nih.gov
5. Nardil (phenelzine sulfate) tablets prescribing information. Parke-Davis (Pfizer) / DailyMed (NLM), 2025. dailymed.nlm.nih.gov
6. Parnate (tranylcypromine) tablets prescribing information. ADVANZ Pharma / DailyMed (NLM), 2025. dailymed.nlm.nih.gov
7. Emsam (selegiline transdermal system) prescribing information. Viatris Specialty / DailyMed (NLM), 2025. dailymed.nlm.nih.gov

Educational information, not medical, tax or legal advice. Decisions about diagnosis, medication and treatment belong with a clinician who knows your history.