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The more acidic and sugary your saliva becomes, the more difficult it is for drugs to be detected in it. So, if you only have 5–10 minutes before you'll be given a mandatory drug swab test, pop in 2 or 3 sour citrus candies. Suck them (rather than chewing) to get as much of the acidic citrus flavoring out of the candies as you can! Chewing on a piece of gum stimulates your saliva production, which will dilute the concentration of any drugs in your saliva. Chewing gum will also change the chemical makeup of your oral fluids, which can make the mouth swab test less effective. If you have a choice between different flavors, opt for a cinnamon or strong citrus flavors. It wouldn't be a bad idea to carry a pack of gum with you to work on a daily basis if you're concerned about surprise swab tests. Peroxide is what's known as an “adulterant”: a chemical that interferes with the swab test's ability to accurately detect drugs in your saliva. Take a gulp of peroxide just before your test, and swish it around inside your mouth for 30 seconds. Then spit it out into the sink. Be careful not to accidentally swallow any of the peroxide. It's can cause internal harm if ingested.  Avoid using alcohol-based mouthwashes, though, as they can lead to a false positive result for alcohol abuse.

Summary:
Suck sour candies to make your saliva more acidic. Chew a couple of pieces of gum to increase your saliva production. Rinse your mouth with hydrogen peroxide 5 minutes before the test.