Famotidine side effects

Key Takeaways

• Common, usually mild side effects: headache, dizziness, constipation, diarrhea, and fatigue.

• Other frequent minor complaints: dry mouth, nausea, vomiting, bloating, and gas.

• Rare but serious reactions include QT prolongation/arrhythmias, liver injury, thrombocytopenia, severe allergic reactions, and seizures.

• Older adults and people with impaired kidney function are more likely to experience CNS effects (confusion, agitation, hallucinations, delirium).

• Watch for palpitations, fainting, jaundice, black stools, unusual bleeding, or signs of anaphylaxis — seek urgent care if these occur.

Common and Mild Side Effects

How common are the everyday complaints from famotidine? Common and mild side effects include headache, dizziness, constipation, and diarrhea. These can appear with short- or long-term use and often improve on their own within days to weeks. Fatigue is also reported. Less frequent complaints include dry mouth, nausea, vomiting, bloating, and gas. Older adults can be more prone to central nervous system symptoms such as agitation or confusion, though those are less common. If symptoms are persistent, worsening, or particularly bothersome, patients should speak with a healthcare professional — a dose change or different therapy may be recommended. Routine testing is not usually needed for isolated mild effects.

Serious and Rare Adverse Reactions

What serious risks should be considered with famotidine? Serious and rare adverse reactions include cardiac, liver, blood, allergic, and neurologic events. Long QT syndrome has been reported and can cause dizziness, palpitations, fainting, or seizures — risk is higher when combined with other QT-prolonging drugs or with electrolyte disturbances. Liver injury can range from mild enzyme elevations to hepatitis or jaundice and may occur at any time. Thrombocytopenia (low platelets) can present with easy bruising, petechiae, or bleeding and requires prompt evaluation. Severe allergic reactions, including anaphylaxis, need emergency treatment. Clinically significant CNS effects such as agitation, delirium, confusion, hallucinations, or seizures are rare but more likely in older people or those with impaired renal function. Any worrying signs should trigger immediate medical assessment.

Central Nervous System and Psychiatric Effects

In addition to the uncommon cardiac, hepatic, hematologic, and allergic events, famotidine has been linked to central nervous system and psychiatric effects that range from mild confusion or dizziness to agitation, hallucinations, delirium, and seizures. Case reports describe confusion, disorientation, and hallucinations occurring more often in elderly patients and in people with kidney impairment, where the drug can accumulate. CNS symptoms may appear alongside common side effects like headache, dizziness, or fatigue. Severe delirium or seizures have required medical care and occasional hospitalization. Clinicians should check renal function and consider patient age when prescribing, watch for new or worsening neuropsychiatric signs, and advise prompt contact with a healthcare provider or urgent care if alarming symptoms arise.

Drug Interactions and Risks for Long QT

Can famotidine raise the chance of dangerous heart-rhythm problems when taken with other medicines? Famotidine can contribute to Long QT and QT prolongation, especially when combined with other QT-prolonging drugs. Known drug interactions include certain antidepressants, antipsychotics, antiarrhythmics, some antibiotics, and some antifungals; clinicians should review all prescription drugs, over‑the‑counter medicines, and supplements. People with congenital long QT, electrolyte imbalances, kidney disease, or age 65 and older face higher risk. Periodic heart-rhythm monitoring and electrolyte checks are recommended during long-term therapy or when adding interacting agents. QT prolongation can lead to ventricular arrhythmias that present as fainting, near-fainting, or seizures — these symptoms require immediate medical attention. Prescribers should evaluate cumulative QT risk before starting famotidine.

Managing Side Effects and When to Seek Help

When should a clinician or patient act on famotidine side effects? Monitor common, short-lived effects (headache, dizziness, mild GI symptoms), but seek medical help if symptoms are severe, persistent, or suggest a serious problem. CNS signs — agitation, confusion, hallucinations, seizures — need prompt evaluation, particularly in people with kidney disease. Report palpitations, fainting, or new chest symptoms as possible signs of long QT. Look for jaundice or dark urine as warning signs of liver injury. Go to emergency care for allergic reactions, black or tarry stools, or vomiting that looks like coffee grounds.

If you notice any serious signs listed above, seek medical attention right away.