A disclosure before we go further: I develop soup cleanse products, so read the evidence sections closely and check my claims against the sources. Where the research is thin, I’ve said so.
The timeline that gives it away
Caffeine withdrawal headaches follow a predictable clock. Onset runs 12 to 24 hours after the last dose, peaks somewhere between 20 and 51 hours out, and resolves within two to nine days. About half of people who stop caffeine abruptly get a headache from it. The mechanism is vascular: caffeine keeps blood vessels in the brain slightly constricted, and when it’s gone, they widen. That rebound in blood flow is what you feel as a headache.
Line that timeline up against a cleanse that starts with your normal morning coffee and nothing after: last dose is roughly 8 or 9am on day one, symptom onset lands 12 to 24 hours later, which is the evening of day one into the morning of day two, and peak intensity hits 20 to 51 hours out, squarely in the middle of day two. That is not a coincidence. It is the same clock caffeine withdrawal runs on for anyone, cleanse or no cleanse. The clock counts from your last dose, so a last cup at 3pm the day before moves the peak earlier, into the first day.
How much caffeine you are stopping
The FDA puts the amount most adults can take without negative effects at 400 milligrams a day. Drinks vary widely. A 12-ounce cup of regular brewed coffee carries between 113 and 247 milligrams of caffeine, black tea about 71, and green tea about 37. Two people who each drink one coffee a day can be on very different doses.
The FDA does not consider caffeine withdrawal dangerous, though it can be unpleasant. Mayo Clinic describes the symptoms as mild for most people and gone within a few days.
The full list of withdrawal symptoms
The DSM-5 recognizes caffeine withdrawal as a diagnosis. Its symptoms are headache, marked fatigue or drowsiness, low mood or irritability, difficulty concentrating, and flu-like symptoms such as nausea and muscle aches, and three or more meet the definition. Most of that list reads like a description of a hard second day of a cleanse. If the headache arrives with fatigue, irritability, and fog, the same clock explains all of them.
What else is stacking on top of it
Caffeine withdrawal explains the timing, but it is rarely acting alone. A soup cleanse also drops your sodium intake substantially, since broth-only eating removes most of the sodium a normal diet supplies from solid food. Fasting itself raises sodium loss in the urine, the natriuresis of fasting, so intake falls while losses rise. Low sodium causes its own headache, along with fatigue and dizziness on standing, and it layers directly on top of the caffeine one and does not replace it. If you haven’t salted your broth properly, day two is where both bills come due at once.
The arithmetic is short. A teaspoon of table salt holds about 2,300 milligrams of sodium, which is the US Daily Value, and a quarter teaspoon holds about 575. One major brand’s regular chicken broth lists 520 milligrams a cup. The guide has you salt every batch for this reason.
The two headaches feel alike and respond to different fixes. Dizziness on standing points to sodium and fluid, and a cup of salted broth answers it. A headache that lifts after a cup of black coffee points to caffeine.
How to taper
The FDA’s advice for anyone cutting back is to do it gradually. I haven’t found a trial that compares taper schedules, so what follows is a reasonable ramp that no study has tested. A week before the cleanse, replace one of every two cups of coffee with decaf. Three days before, replace the rest. Moving from coffee to black tea in one step cuts the caffeine per 12-ounce cup by 37 to 71 percent, and Mayo Clinic also suggests brewing tea for less time or switching to herbal tea. Check pain reliever labels, since some contain caffeine, and Mayo suggests caffeine-free ones while you cut back.
Keep some coffee in the routine, at least for your first cleanse. Nothing about the straw test rules out black coffee, and there is a good case for not stacking a caffeine withdrawal headache on top of everything else a first cleanse asks of you.
What helps on the day
Salt your broth properly, every batch. This bears repeating because it is the detail people skip. A pinch of sea salt in your water and a properly seasoned broth do a lot of work here.
If the headache still shows up, it often eases by day three, which lines up with where caffeine withdrawal symptoms peak and start to fade. The headache is no sign the cleanse is going wrong.
When it isn’t this
A headache that keeps getting worse, or that comes with marked dizziness or a racing heart, is no longer caffeine withdrawal. That is the same stop-if-unwell threshold that applies to the rest of a cleanse: end it and eat a proper meal.
A sudden, severe headache, or one that comes with fever, a stiff neck, confusion, weakness, or changes in speech or vision, needs urgent medical care. So does any headache after a head injury.
If you drink coffee daily and the headache arrives on day two, the clock points at caffeine. The cleanse happened to be what moved the due date up.
Common questions
- Why do I get a headache on day two of a soup cleanse?
- Caffeine withdrawal is the first suspect. Onset runs 12 to 24 hours after the last dose and the peak comes 20 to 51 hours out, which lands on day two. Low sodium adds to it.
- How long does a caffeine withdrawal headache last?
- Onset runs 12 to 24 hours after the last dose, the peak comes between 20 and 51 hours, and symptoms resolve within two to nine days. Mayo Clinic describes most as mild and gone within a few days.
- Should you drink coffee during a soup cleanse?
- Nothing in the straw test rules out black coffee, and keeping some in the routine avoids stacking a withdrawal headache on top of a first cleanse.