Can I Start Methylene Blue 3 Weeks After Stopping Fluoxetine?

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Three weeks is a good start, but it isn't quite long enough for fluoxetine to be considered out of your system, and methylene blue happens to be one of the product where that timing really matters.

Fluoxetine's prescribing information calls for waiting at least five weeks after the last dose before starting a monoamine oxidase inhibitor (MAOI), and methylene blue belongs to that group.

Why Methylene Blue and Fluoxetine Are a Risky Pair

Most people know methylene blue as a dye or as the hospital treatment for methemoglobinemia, a blood condition that keeps red cells from carrying oxygen properly. It has become increasing popular as a dietary supplement as well.

What's less widely known is that it is also a potent, reversible inhibitor of monoamine oxidase A, the enzyme your body uses to break down serotonin.

Fluoxetine (Prozac) works by blocking serotonin reuptake, so it raises serotonin activity from the other direction. Put the two together and serotonin can climb high enough to cause serotonin syndrome, which shows up as agitation, confusion, sweating, fever, a racing heart, tremor, muscle stiffness, and twitching, and in severe cases it can be life-threatening.

The FDA issued a safety warning about this combination back in 2011, and case reports since then have described serotonin syndrome in people on fluoxetine who received methylene blue in the hospital.

Why Three Weeks Isn't Enough With Fluoxetine Specifically

Fluoxetine is the outlier among the SSRIs when it comes to how long it lingers.

The drug itself has a half-life of roughly four to six days, and its active metabolite, norfluoxetine, sticks around even longer, with a half-life of one to two weeks. That's why the label repeatedly uses a five-week window for interactions after the drug is stopped, including a five-week wait before starting an MAOI, and it treats a person who stopped fluoxetine in the past five weeks the same way it treats someone still taking it.

Had you been on sertraline or escitalopram, a two-week break would typically be the standard, but with fluoxetine you're only a bit past the halfway point at three weeks, and there is very likely still meaningful drug in your body.

What a Small Oral Dose Changes, and What It Doesn't

I understand the thinking that a small oral dose might be a different situation, and to be fair, most of the published serotonin syndrome cases involved intravenous methylene blue at hospital doses.

The approved IV product (ProvayBlue) is given at 1 mg/kg, which works out to around 70 mg for an average adult, and cases have generally involved doses in that range or higher. The trouble is that we don't have good data on where the safe floor is.

Methylene blue inhibits MAO-A at fairly low concentrations, oral products sold online for general wellness aren't FDA-approved for that use, and their purity and actual milligram content can vary quite a bit, so a 'small dose' isn't as well defined as it sounds. The absence of case reports at low oral doses isn't the same as evidence that it's safe, particularly while fluoxetine and norfluoxetine are still on board.

One more thing worth raising with your prescriber is the reason you stopped fluoxetine and whether there's any chance you'll be restarting it or another antidepressant.

If you begin methylene blue and then need to go back on an SSRI, you'd be facing the same interaction in reverse, and that's a conversation better had before either step. Your doctor or pharmacist can also weigh in on the product you're considering and what you're hoping to get from it. You can read more about both medicines on our fluoxetine and methylene blue pages.

Final Words

To summarize, at three weeks off fluoxetine, you're not yet past the five-week washout that its label calls for before an MAOI like methylene blue, so this isn't a combination I'd feel comfortable calling safe right now, even at a low oral dose.

Please talk with your doctor or pharmacist before starting, share the specific product and dose you have in mind, and know the warning signs of serotonin syndrome so you can seek care quickly if they ever appear. Feel free to write back if you have follow-up questions.

Thanks!