Midol is an OTC drug that contains three active substances: acetaminophen (500 mg), caffeine (60 mg) and pyrilamine maleate (15 mg). It is used to relieve symptoms related to menstrual periods, such as pain and cramps.  Midol can also be used off-label to help people who have used drugs mentioned above to pass urine drug screening tests.
Scientific evidence which supports using this method to pass drug test lies in the fact that caffeine (one of the Midol’s active ingredients) is a potent diuretic. Although it is true that you can take a cup of coffee or tea (which are known to be rich in caffeine), caffeine contained in Midol exerts more potent diuretic effect than coffee or tea.
Caffeine decreases vasoconstriction of blood vessels in kidneys, thus increasing glomerular renal filtration rate, which further results in the diuretic effect. Also, caffeine also boosts sodium excretion via urine which also increases diuresis. 
Taking caffeine (Midol) along with drinking lots of water can be very effective at purging the body of the drug metabolites. Unfortunately, there are no clinical studies that confirm this method as effective in cleaning the urine, and they will probably never be conducted, as no one wants to show people how to pass a drug urine test.
What You Will Need
There are only two things you’re going to need for this method:
- A lot of water. It is essential to drink sufficient amounts of water as Midol will not work if you don’t. It doesn’t matter whether you are taking sparkling or regular water.
- Midol pills. Midol can be purchased without a prescription, and you can find it in almost every pharmacy.
Don’t be a worry if you’re a man and you’re going to take Midol. Midol is mostly prescribed in women, but it can also safely be used in men as well.
How To Use
First of all, you should start taking a sufficient amount of water as soon as possible. You cannot expect to remove all effects and signs of drug use in a short period, but you can easily flush your system and clean your urine from any drug metabolites, so the drug test will not show that you’ve been using drugs. To flush your system, you must start drinking lots of water as soon as you find out that you’re going to be tested for drugs.
The second step is to take one Midol pill six to eight times a day (every four or three hours). Taking Midol in this way will make you pee more often, thus leading to increased excretion of drug metabolites which results in their decreased and undetectable levels in the urine.
Maximum daily dosage for Midol is eight tablets. You should never exceed this dose as it increases your risk of side effects. 
Why It Can Fail
Despite the fact that many claims that taking Midol along with increased water intake may help you pass a drug test, there is no guarantee that this method will work for you. In the end, the success of this method will depend on one’s individual characteristics (e.g., how effective your kidneys are in eliminating metabolites) and other relevant factors such as how long have you been doing drugs.
Bear in mind that this method doesn’t help you in eliminating toxins, but only speed up urination and decrease the concentration of drug metabolites in urine.
This method can also fail if you started taking Midol too late (e.g., only a few hours before testing).
Like any other drug, Midol can also cause side effects. Following side effects have been reported in people taking Midol:
- Abdominal cramps.
- Liver damage, accompanied by jaundice and elevated blood levels of liver enzymes.
- Tachycardia (rapid heart rate).
- Agranulocytosis (extremely low white blood cell count). Agranulocytosis may waken your immune system so you must report to your doctor if you’re experiencing flu-like symptoms after taking Midol.
- Thrombocytopenia (low blood platelet count). You should inform your doctor if you notice easy or excessive bruising as this may be a sign of thrombocytopenia.
- Increased sweating.
- Dry mouth, nose or throat.
- Photosensitivity (increased sensitivity to sunlight).
- Ringing in the ears.
- Visual disturbances.
Cases of severe allergic reactions, such as Stevens-Johnson syndrome (severe toxic skin reaction) and anaphylactic shock have also been reported with the use of Midol. Therefore, you must contact your doctor right away if you notice any changes on your skin or swelling of the lips, tongue or face.
Also, Midol may cause acute liver failure that can be fatal, so you should inform your doctor immediately if you notice signs of liver damage (pain in the right, upper abdomen, jaundice, loss of appetite and nausea). [13, 14]