What the label lists and what reports show

Fosfomycin side effects

Fosfomycin's FDA label: “Clinical Trials: In clinical studies, drug related adverse events which were reported in greater than 1% of the fosfomycin-treated study population are listed below: Drug-Related Adverse Events (%) in Fosfomycin and Comparator Populations Adverse Events …” FAERS holds 598 reports naming it through July 30, 2026; the reaction reported most often, leaving out the conditions it is used for, product-use terms and outcomes, is nausea (62 reports).

Generic listed

Check it at the source: the fosfomycin FDA label on DailyMed (effective April 9, 2026, Aucta Pharmaceuticals, Inc.); the FDA FAERS public dashboard.

What does the label list?

From the label: adverse reactions
Clinical Trials: In clinical studies, drug related adverse events which were reported in greater than 1% of the fosfomycin-treated study population are listed below: Drug-Related Adverse Events (%) in Fosfomycin and Comparator Populations Adverse Events Fosfomycin N=1233 Nitrofurantoin N=374 Trimethoprim/ sulfamethoxazole N=428 Ciprofoxacin N=455 Diarrhea 9.0 6.4 2.3 3.1 Vaginitis 5.5 5.3 4.7 6.3 Nausea 4.1 7.2 8.6 3.4 Headache 3.9 5.9 5.4 3.4 Dizziness 1.3 1.9 2.3 2.2 Asthenia 1.1 0.3 0.5 0.0 Dyspepsia 1.1 2.1 0.7 1.1 In clinical trials, the most frequently reported adverse events occurring in > 1% of the study population regardless of drug relationship were: diarrhea 10.4%, headache 10.3%, vaginitis 7.6%, nausea 5.2%, rhinitis 4.5%, back pain 3.0%, dysmenorrheal 2.6%, pharyngitis 2.5%, dizziness 2.3%, abdominal pain 2.2%, pain 2.2%, dyspepsia 1.8%, asthenia 1.7%, and rash 1.4%.

Table 3 Adverse Reactions Occurring in 2% or Greater of Patients with cUTI Receiving CONTEPO in Trial 1

This table is printed in the Contepo label published by Meitheal Pharmaceuticals Inc. of November 4, 2025; the label quoted above does not print one.

Reaction	CONTEPO N=233 %	Piperacillin/Tazobactam N=231 %
Nausea	4.3	1.3
Diarrhea	3.9	4.8
Vomiting	3.9	0.4
Transaminase elevations a	10.3	4.8
Hypokalemia	9.9	1.7
Hypophosphatemia	2.1	0.0
Hypocalcemia	3.9	2.6
Hypernatremia	3.4	0.9
Neutropenia b	6.4	3.9
Headache	2.6	2.2

Rows and numbers as the label prints them, under its own column headings (the first rows of a longer table where it runs on). A reaction in a trial table is not necessarily caused by the medicine, and trials differ from everyday use.

From the label: adverse reactions, continued
Clinical Trials: In clinical studies, drug related adverse events which were reported in greater than 1% of the fosfomycin-treated study population are listed below: Drug-Related Adverse Events (%) in Fosfomycin and Comparator Populations Adverse Events Fosfomycin N=1233 Nitrofurantoin N=374 Trimethoprim/ sulfamethoxazole N=428 Ciprofoxacin N=455 Diarrhea 9.0 6.4 2.3 3.1 Vaginitis 5.5 5.3 4.7 6.3 Nausea 4.1 7.2 8.6 3.4 Headache 3.9 5.9 5.4 3.4 Dizziness 1.3 1.9 2.3 2.2 Asthenia 1.1 0.3 0.5 0.0 Dyspepsia 1.1 2.1 0.7 1.1 In clinical trials, the most frequently reported adverse events occurring in > 1% of the study population regardless of drug relationship were: diarrhea 10.4%, headache 10.3%, vaginitis 7.6%, nausea 5.2%, rhinitis 4.5%, back pain 3.0%, dysmenorrheal 2.6%, pharyngitis 2.5%, dizziness 2.3%, abdominal pain 2.2%, pain 2.2%, dyspepsia 1.8%, asthenia 1.7%, and rash 1.4%. The following adverse events occurred in clinical trials at a rate of less than 1%, regardless of drug relationship: abnormal stools, anorexia, constipation, dry mouth, dysuria, ear disorder, fever, flatulence, flu syndrome, hematuria, infection, insomnia, lymphadenopathy, menstrual disorder, migraine, myalgia, nervousness, paresthesia, pruritus, SGPT increased, skin disorder, somnolence, and vomiting. …

Source: FDA drug label, Aucta Pharmaceuticals, Inc., effective April 9, 2026 (SPL set 4f206750-8126-99a3-e063-6294a90ade4c), via openFDA; the full label on DailyMed

What do FAERS reports show?

598 reports list fosfomycin among the medicines taken, each a report of something that happened, not proof the medicine caused it; 31 are coded as a death and 284 as a hospital stay. Counts follow how widely a medicine is used and watched, and they are not a measure of how risky it is. Of the 21 reactions below, 9 are named by the same term (in US spelling) in the label's adverse reactions, warnings or patient leaflet; a reaction the label does not name may still be there under another word, and a report does not show that the medicine caused it.

Reports received each year

The 25 most reported reactions

Nausea (named in the label)62
Diarrhoea (named in the label)54
Dizziness (named in the label)53
Dyspnoea51
Off Label Use (a use or a product term, not a reaction)51
Urinary Tract Infection (a use or a product term, not a reaction)46
Fatigue43
Vomiting (named in the label)42
Asthenia (named in the label)30
Headache (named in the label)29
Arthralgia28
Covid-1928
Malaise27
Pain27
Cystitis (a use or a product term, not a reaction)24
Gait Disturbance24
Neutropenia (named in the label)24
Pruritus (named in the label)24
Tachycardia24
Abdominal Pain (named in the label)23
Abdominal Pain Upper23
Decreased Appetite22
Hypotension22
Product Use Issue (a use or a product term, not a reaction)22
Erythema21

Source: FDA Adverse Event Reporting System (FAERS) via openFDA, reports through July 30, 2026; reactions as MedDRA preferred terms

What next?

Fosfomycin: the full record: label, generics, price, shortages, recalls
Report a side effect to the FDA: MedWatch
Side effects hub: the most reported medicines and reactions