This is the time it takes for the drug level in your plasma to be reduced by half. So half of the Zantac is out of your system in 3 hours, leaving half. Half of the remaining half is out in the next 3 hours leaving 1/4. Half of the remaining 1/4 is out in the next 3 hours leaving 1/8, etc. The half-life of ranitidine (Zantac) is about 3 hours, so half of it is out of your system in 3 hours, leaving half. Half of the remaining half is out in the next 3 hours leaving 1/4. half of the remaining 1/4 is out in the next 3 hours leaving 1/8, etc. Zantac is the brand name of the generic compound Ranitidine. Generally, a 150 mg ranitidine tablet has a elimination half-life of 2.5 - 3 hours. How long alcohol stays in your urine or system can be a big concern to some people for many reasons. If you have a required urine test for drugs in your job or if you need to take a test as part of a job interview you may be concerned about the amount of required time needed for alcohol to leave your system and show no trace in your urine. You could also have had a nights drinking and want to. You need to discuss this with whoever is requiring the drug test so they know that you're on a medication for acid reflux that's interfering with your drug testing, and also discuss it with the medical staff that are conducting the drug test. I took 1 dose 2 nights ago and more How long does it take for Zantac (ranitidine) 150 to completely leave your system? I took 1 dose 2 nights ago and am having abdominal pain and I'm very lightheaded I took 1 dose 2 nights ago and am having abdominal pain and I'm very lightheaded Hello, Welcome to justanswer.com and thanks for your question. Well Omeprazole effects last for 3-5 days after discontinuation of therapy. And it is advised not to stop Omeprazole abruptly. 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. How long does it take zantac to leave your system? Zantac is the brand name of the generic compound Ranitidine. Generally, a 150 mg ranitidine tablet has a elimination half-life of 2.5 - 3 hours. Doctors give trusted answers on uses, effects, side-effects, and cautions: Dr. Wartenberg on how long does zantac stay in your system: This varies with last dose taken, usually 3-4 days, & up to 1 week if high dose..