Health Guide
Drug Guide

Histamine h2 antagonist (Oral route, injection route, intravenous route)

Brand Names:

Dosage Forms:

Uses of This Medicine:

Histamine H2-receptor antagonists, also known as H2-blockers, are used to treat duodenal ulcers and prevent their return. They are also used to treat gastric ulcers and for some conditions, such as Zollinger-Ellison disease, in which the stomach produces too much acid. In over-the-counter (OTC) strengths, these medicines are used to relieve and/or prevent heartburn, acid indigestion, and sour stomach. H2-blockers may also be used for other conditions as determined by your doctor.

H2-blockers work by decreasing the amount of acid produced by the stomach.

H2-blockers are available both over-the-counter (OTC) and with your doctor's prescription.

Once a medicine has been approved for marketing for a certain use, experience may show that it is also useful for other medical problems. Although these uses are not included in product labeling, H2-blockers are used in certain patients with the following medical conditions:

Before Using This Medicine:


Tell your doctor if you have ever had any unusual or allergic reaction to medicines in this group or any other medicines. Also tell your health care professional if you have any other types of allergies, such as to foods dyes, preservatives, or animals. For non-prescription products, read the label or package ingredients carefully.


This medicine has been tested in children and, in effective doses, has not been shown to cause different side effects or problems than it does in adults when used for short periods of time.

Older adults

Confusion and dizziness may be especially likely to occur in elderly patients, who are usually more sensitive than younger adults to the effects of H2-blockers.


H2-blockers have not been studied in pregnant women. In animal studies, famotidine and ranitidine have not been shown to cause birth defects or other problems. However, one study in rats suggested that cimetidine may affect male sexual development. More studies are needed to confirm this. Also, studies in rabbits with very high doses have shown that nizatidine causes miscarriages and low birth weights. Make sure your doctor knows if you are pregnant or if you may become pregnant before taking H2-blockers.


Cimetidine, famotidine, nizatidine, and ranitidine pass into the breast milk and may cause unwanted effects, such as decreased amounts of stomach acid and increased excitement, in the nursing baby. It may be necessary for you to take another medicine or to stop breast-feeding during treatment. Be sure you have discussed the risks and benefits of the medicine with your doctor.

Other medicines

Although certain medicines should not be used together at all, in other cases two different medicines may be used together even if an interaction might occur. In these cases, your doctor may want to change the dose, or other precautions may be necessary. When you are taking any of these medicines, it is especially important that your healthcare professional know if you are taking any of the medicines listed below. The following interactions have been selected on the basis of their potential significance and are not necessarily all-inclusive.

Using medicines in this class with any of the following medicines is not recommended. Your doctor may decide not to treat you with a medication in this class or change some of the other medicines you take.

Using medicines in this class with any of the following medicines is usually not recommended, but may be required in some cases. If both medicines are prescribed together, your doctor may change the dose or how often you use one or both of the medicines.

Other interactions

Certain medicines should not be used at or around the time of eating food or eating certain types of food since interactions may occur. Using alcohol or tobacco with certain medicines may also cause interactions to occur. Discuss with your healthcare professional the use of your medicine with food, alcohol, or tobacco.

Other medical problems

The presence of other medical problems may affect the use of medicines in this class. Make sure you tell your doctor if you have any other medical problems, especially:

Proper Use of This Medicine:

For patients taking the nonprescription strengths of these medicines for heartburn, acid indigestion, and sour stomach:

For patients taking the prescription strengths of these medicines for more serious problems:

It may take several days before this medicine begins to relieve stomach pain. To help relieve this pain, antacids may be taken with the H2-blocker, unless your doctor has told you not to use them. However, you should wait one-half to one hour between taking the antacid and the H2-blocker. Take this medicine for the full time of treatment, even if you begin to feel better. Also, it is important that you keep your appointments with your doctor for check-ups so that your doctor will be better able to tell you when to stop taking this medicine.

For patients taking famotidine chewable tablets:

For patients taking famotidine oral disintegrating tablets:

For patients taking ranitidine effervescent tablets:


The dose medicines in this class will be different for different patients. Follow your doctor's orders or the directions on the label. The following information includes only the average doses of these medicines. If your dose is different, do not change it unless your doctor tells you to do so.

The amount of medicine that you take depends on the strength of the medicine. Also, the number of doses you take each day, the time allowed between doses, and the length of time you take the medicine depend on the medical problem for which you are using the medicine.

Missed dose

If you miss a dose of this medicine, take it as soon as possible. However, if it is almost time for your next dose, skip the missed dose and go back to your regular dosing schedule. Do not double doses.


Store the medicine in a closed container at room temperature, away from heat, moisture, and direct light. Keep from freezing.

Keep out of the reach of children.

Do not keep outdated medicine or medicine no longer needed.

Precautions While Using This Medicine:

Some tests may be affected by this medicine. Tell the doctor in charge that you are taking this medicine before:

Remember that certain medicines, such as aspirin, and certain foods and drinks (e.g., citrus products, carbonated drinks) irritate the stomach and may make your problem worse.

Cigarette smoking tends to decrease the effect of H2-blockers by increasing the amount of acid produced by the stomach. This is more likely to affect the stomach's nighttime production of acid. While taking H2-blockers, stop smoking completely, or at least do not smoke after taking the last dose of the day.

Drinking alcoholic beverages while taking an H2-receptor antagonist has been reported to increase the blood levels of alcohol. You should consult your health care professional for guidance.

Check with your doctor if your ulcer pain continues or gets worse.

Side Effects of This Medicine:

Along with its needed effects, a medicine may cause some unwanted effects. Although not all of these side effects may occur, if they do occur they may need medical attention.

Check with your doctor as soon as possible if any of the following side effects occur:

Abdominal pain
back, leg, or stomach pain
bleeding or crusting sores on lips
blistering, burning, redness, scaling, or tenderness of skin
blisters on palms of hands and soles of feet
changes in vision or blurred vision
coughing or difficulty in swallowing
dark-colored urine
fast, pounding, or irregular heartbeat
fever and/or chills
flu-like symptoms
general feeling of discomfort or illness
inflammation of blood vessels
joint pain
light-colored stools
mood or mental changes, including anxiety, agitation, confusion, hallucinations (seeing, hearing, or feeling things that are not there), mental depression, nervousness, or severe mental illness
muscle cramps or aches
nausea, vomiting, or loss of appetite
peeling or sloughing of skin
red or irritated eyes
shortness of breath
skin rash or itching
slow heartbeat
sore throat
sores, ulcers, or white spots on lips, in mouth, or on genitals
sudden difficult breathing
swelling of face, lips, mouth, tongue, or eyelids
swelling of hands or feet
swollen or painful glands
tightness in chest
troubled breathing
unusual bleeding or bruising
unusual tiredness or weakness
unusually slow or irregular breathing
yellow eyes or skin

Some side effects may occur that usually do not need medical attention. These side effects may go away during treatment as your body adjusts to the medicine. Also, your health care professional may be able to tell you about ways to prevent or reduce some of these side effects. Check with your health care professional if any of the following side effects continue or are bothersome or if you have any questions about them:

Less common or rare
decrease in sexual desire
decreased sexual ability (especially in patients with Zollinger-Ellison disease who have received high doses of cimetidine for at least 1 year)
difficult urination
dryness of mouth or skin
increased or decreased urination
increased sweating
loss of hair
ringing or buzzing in ears
runny nose
swelling of breasts or breast soreness in females and males
trouble in sleeping

Not all of the side effects listed above have been reported for each of these medicines, but they have been reported for at least one of them. All of the H2-blockers are similar, so any of the above side effects may occur with any of these medicines.

Other side effects not listed may also occur in some patients. If you notice any other effects, check with your healthcare professional.

Call your doctor for medical advice about side effects. You may report side effects to the FDA at 1-800-FDA-1088.

Last Updated: 10/12/2016

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