It’s widely known that modafinil is commonly taken to sustain energy throughout the day. It was designed to prevent people from falling asleep, so it has to work for a while. Yet how long does modafinil actually last and stay in your body? And what does that have to do with the effects of the pill itself?
A number that’s often thrown around when this question comes up is the “half-life” of the medicine. The term “half-life” refers to the time it takes for there to be half of a given amount of a substance. The term originates with nuclear physics, where an unstable element decays into another one at a fixed rate and thus makes it easy to calculate its half-life. For instance, if you had 100kg of cesium-137, a common nuclear waste isotope, you’d have only 50kg after 30 years. That’s one half-life, and if you wait another, you’d get 25kg in 60 years, and so on.
In the body however the process gets trickier, because we’re not talking about a stable, constant, observable nuclear process. The human body has many more variables that make it hard to pin down the exact process. One way that medical researchers determine the half-life of a medicine is to measure its concentration in the patient’s blood. Seeing as it’s the blood that carries medicine to the places it’s needed, it makes sense that we should measure its content there.
Modafinil reaches peak blood plasma concentrations quickly: In about 2-3 hours after taking the pill you will be at maximum modafinil capacity. So how long will it stay there? To understand this we have to talk about how modafinil is composed of two enantiomers, or mirror versions of the same substance. Even though they are nearly identical forms of the same compound, they can have different effects on the body. In modafinil’s case the pill you take is a 50/50 mixture of the R and S enantiomers, and their half lives are different: 15 hours for the R and 4 for the S.
So, just take 15 and 4, get 19, divide by two and we’ve got our average half-life, right? Well it’s still not quite that simple because the R enantiomer is the one that’s responsible for most of the function of modafinil. This is so true that they’ve recently started selling only the R enantiomer on its own as “armodafinil”. So in reality modafinil’s half-life is closer to 10-12 hours, probably less than twelve.
Why does the half-life matter so much? Effectively it tells us when the medicine should be wearing off. By the half-life time, it’s literally half as potent as it was before, which can mean that it no longer affects certain systems in your body. And in medicine a half-life is not necessarily linear, it can come very suddenly. It serves as a useful market to note where and when your medicine is going to stop working and it helps doctors plan dosage schedules.
Just to speak from personal experience, I find that around 10 hours after I take modafinil it’s less powerful. In fact, it’s usually right around that time that I start feeling a little tired. By 12 hours, I feel like I could sleep pretty soon, though not quite yet. For me it’s about 15 hours before I can sleep, and at that point in time less than 50mg of my original 200mg is still in my body. Most users report similar findings.
How long do large doses of modafinil last?
If you take bigger doses the same rules apply. For instance, if you took 400mg of modafinil you’ll be down to about half of that in roughly 10 hours, meaning that you still have 200mg in your system and you should be able to continue working on that dose. That dose will take another 10 hours to reduce to 100mg. So a large 400mg dose could keep you active for an entire 24-hour day. As with everything in the human body it gets more complicated: You build up short-term tolerance to virtually every drug, reducing its potency as you go. This is different from the long-term tolerance which prevents you from feeling the same effects day after day over the course of a long time. Short-term tolerance is very short-term, perhaps within the same hour or so. Eventually you may notice that your extra dose isn’t having an equal effect, and this is normal. Plus, as you’ve been working hard the whole day, that extra modafinil is making up for a lot of exhaustion, and there’s only so much it can do.
400mg a day is often linked by users to an 18 hour work day, perhaps a double shift of a heavy duty study session.
So how long does modafinil really last?
By all accounts a 200mg dose of modafinil should give you peak performance for at least 8 hours. There should be another 2-4 hours of reduced effects, but still potent enough for the pill to do its job. After that, the medicine is mostly out of your system and its effects will be limited. Bear in mind that individual metabolisms may vary, and the rate of absorption can be affected by eating a large meal before taking a pill, for instance.
Make sure that you plan your modafinil days well in order to get the most out of your dose.