From the Guidelines
Pepcid (famotidine) can cause several side effects, though most people tolerate it well, with common side effects including headache, dizziness, constipation or diarrhea, and mild stomach discomfort, as noted in the FAMOUS trial 1.
Common Side Effects
- Headache
- Dizziness
- Constipation or diarrhea
- Mild stomach discomfort Less frequently, users may experience fatigue, muscle pain, or changes in taste.
Rare but Serious Side Effects
Rare but serious side effects that require immediate medical attention include:
- Irregular heartbeat
- Confusion
- Hallucinations
- Seizures
- Unusual bleeding or bruising
- Signs of allergic reaction such as rash, itching, swelling, severe dizziness, or difficulty breathing Elderly patients may be more susceptible to side effects, particularly confusion. Pepcid works by reducing stomach acid production by blocking histamine H2 receptors in the stomach, which explains why it can occasionally cause systemic effects beyond the digestive system. If you experience persistent or severe side effects while taking Pepcid, contact your healthcare provider rather than discontinuing the medication abruptly, as they may recommend adjusting your dosage or switching to an alternative treatment. It is also worth noting that, according to a more recent study 1, H2-receptor antagonists like famotidine can be given simultaneously or 12 h apart at a dose not exceeding that equivalent to famotidine 40 mg, and this study provides more general information about drug interactions, although it is not directly related to the side effects of Pepcid.
From the FDA Drug Label
The following adverse reactions occurred in greater than or equal to 1% of Famotidine-treated patients: headache, dizziness and constipation The following other adverse reactions were reported in less than 1% of patients in clinical trials: Body as a Whole: fever, asthenia, fatigue Cardiovascular: palpitations Gastrointestinal: elevated liver enzymes, vomiting, nausea, abdominal discomfort, anorexia, dry mouth Hematologic: thrombocytopenia Hypersensitivity: orbital edema, rash, conjunctival injection, bronchospasm Musculoskeletal: musculoskeletal pain, arthralgia Nervous System/Psychiatric: seizure, hallucinations, depression, anxiety, decreased libido, insomnia, somnolence Skin: pruritus, dry skin, flushing Special Senses: tinnitus, taste disorder Other: impotence The following adverse reactions have been reported during post-approval use of famotidine. Cardiovascular: arrhythmia, AV block, prolonged QT interval Gastrointestinal: cholestatic jaundice, hepatitis Hematologic: agranulocytosis, pancytopenia, leukopenia Hypersensitivity: anaphylaxis, angioedema, facial edema, urticaria Musculoskeletal: rhabdomyolysis, muscle cramps Nervous System/Psychiatric: confusion, agitation, paresthesia Respiratory: interstitial pneumonia Skin: toxic epidermal necrolysis/Stevens-Johnson syndrome
The side effects of Pepcid (Famotidine) include:
- Common side effects (occurring in ≥ 1% of patients):
- Headache
- Dizziness
- Constipation
- Less common side effects (occurring in < 1% of patients):
- Body as a Whole: fever, asthenia, fatigue
- Cardiovascular: palpitations
- Gastrointestinal: elevated liver enzymes, vomiting, nausea, abdominal discomfort, anorexia, dry mouth
- Hematologic: thrombocytopenia
- Hypersensitivity: orbital edema, rash, conjunctival injection, bronchospasm
- Musculoskeletal: musculoskeletal pain, arthralgia
- Nervous System/Psychiatric: seizure, hallucinations, depression, anxiety, decreased libido, insomnia, somnolence
- Skin: pruritus, dry skin, flushing
- Special Senses: tinnitus, taste disorder
- Other: impotence
- Postmarketing side effects:
- Cardiovascular: arrhythmia, AV block, prolonged QT interval
- Gastrointestinal: cholestatic jaundice, hepatitis
- Hematologic: agranulocytosis, pancytopenia, leukopenia
- Hypersensitivity: anaphylaxis, angioedema, facial edema, urticaria
- Musculoskeletal: rhabdomyolysis, muscle cramps
- Nervous System/Psychiatric: confusion, agitation, paresthesia
- Respiratory: interstitial pneumonia
- Skin: toxic epidermal necrolysis/Stevens-Johnson syndrome 2
From the Research
Side Effects of Pepcid (Famotidine)
The side effects of Pepcid (Famotidine) have been studied in various research papers. According to the studies, the overall number of side-effects of the H2-receptor antagonists, including Famotidine, is in the range of 2-3% and no irreversible adverse effects are known 3.
- Common side effects include:
- Headache
- Dizziness
- Constipation
- Diarrhea These side effects have been observed only occasionally 3.
- Other reported side effects include:
- Abdominal pain upper
- Abdominal discomfort
- Dyspepsia
- Liver disorder
- Gastrooesophageal reflux disease
- Rhabdomyolysis These side effects are consistent with the drug instructions 4.
- Unreported side effects that have been found through a disproportionality analysis of the FDA Adverse Event Reporting System (FAERS) database include:
- Cerebral infarction
- Hypocalcaemia
- Hallucination
- Visual
- Hypomagnesaemia
- Hypoparathyroidism
- Diabetes insipidus
- Vulvovaginal candidiasis
- Retro-orbital neoplasm
- Neuroblastoma recurrent
- Malignant cranial nerve neoplasm These side effects suggest the need for prospective clinical studies to confirm these results and explain their relationships 4.
- Post-marketing studies have shown that H2-receptor blockers, including Famotidine, have a low incidence of adverse reactions (1-2% of patients) and are very effective in the treatment of peptic ulcers 5.
Pharmacokinetics and Pharmacodynamics
Famotidine is a competitive histamine H2-receptor antagonist that inhibits gastric acid secretion 6. Its main pharmacodynamic effect in humans is the inhibition of gastric acid secretion, with dose-related suppression of basal and stimulated gastric acid output 6. The drug is eliminated primarily through the kidneys, with an average elimination half-life of 2.8 hours in healthy subjects 6.
Safety Profile
The safety profile of Famotidine has been assessed in several studies, with results indicating that it is generally well tolerated 3, 7. However, the drug may cause severe toxicity to organ systems, including the blood system, digestive system, and urinary system 4.