How long does it take for ranitidine to work. Common Questions and Answers about How long does it take for ranitidine to work. zantac. It was a couple of years ago and haven touched ranitidine since. Just went in to speak to my doctor about it again to see if they could look into it more to make sure. He said it was almost impossible and that I had to have had something else in my system to. Zantac is used to treat and prevent ulcers in the stomach and intestines. It also treats conditions in which the stomach produces too much acid. Zantac received an overall rating of 7 out of 10 stars from 30 reviews. See what others have said about Zantac, including the effectiveness, ease of use and side effects. Doctors give unbiased, trusted information on the benefits and side effects of Ranitidine to treat Gastritis: Dr. Jatoi on how long it takes zantac to work for gastritis: Or less if it's gonna work. Search How to use Zantac 75. To treat heartburn and acid indigestion, take 1 tablet with a glass of water as needed, unless otherwise directed by your doctor. How does Zantac ® work? How long will it take before I experience relief? How long will it take before I experience relief? Zantac ® relieves heartburn in 30 to 60 minutes and controls acid for up to 12 hours. When using Zantac to treat heartburn, it takes 30 minutes to work, according to Zantacotc.com. People who are using Zantac to promote stomach ulcer healing notice a difference within 8 weeks, Drugs.com states. i take zantac 75 and recently took a drug test and tested positive for meth, i have never done meth nor do i want to.. Look ,I absolutely know that zantac will cause a false positive for meth! 75 mg orally once daily ( 30 to 60 minutes before a meal). The dose may be increased to 75 mg twice daily if needed. Maximum duration of therapy if self-medicating is 14 days. The dose may be increased to 75 mg twice daily if needed.