Drug · single active ingredient
Melengestrol Acetate: adverse event reports
All products with this active ingredient · 5 FDA-approved applications in the Green Book
- Mostly cattle reports
- Oral route most often
- Brands masked by FDA
Between November 1991 and November 2025 FDA received 776 adverse event reports listing a drug with melengestrol acetate as the recorded active ingredient. The Green Book lists 5 FDA-approved applications with this single active ingredient.
openFDA masks the brand and manufacturer in every report, so these figures describe the ingredient across all products and cannot be attributed to a brand.
In the 12 months to March 2026, 13 reports named it, down 32% from 19 in the 12 months before. FDA posts reports quarterly with a delay of three to six months, so the newest months are incomplete and usually grow in later releases. Over its whole reporting history that is about 23 reports a year and 0.1% of all 1,357,245 reports (2.4% of all cattle reports). How many animals received it is not published, so a count says nothing about how often a problem occurs per dose.
The most frequently coded terms are ineffective, estrus suppressio (66.9%), inappropriate preparation of medication (12%) and lack of efficacy - NOS (10.7%). A report can list several signs, so shares add to more than 100%; 149 different terms appear across these reports.
95.9% of reports concern cattle. Not every report describes illness: 25.6% were filed wholly or partly as lack of expected effectiveness. Of reports that state seriousness, 22.3% were classed as serious, and 10.8% of all reports record a death or euthanasia as an outcome, as reported. FDA has not necessarily determined whether any drug played a part.
Monthly reports by species, five years
Reports by the month FDA received them. Each panel has its own scale; the peak month is printed at the top right. The newest months are incomplete because FDA posts reports with a delay of three to six months.
Reports by year received
2025 covers reports received through March 2026 only.
Signs listed in reports
share of melengestrol acetate reports listing the termall cattle reports
- Ineffective, estrus suppressio[legacy FDA term: the product did not have the expected effect (estrus suppressio)]66.9%519
- Lack of efficacy - NOS[the product did not have the expected effect]10.7%83
- Death6.4%50
- No sign[no clinical sign was reported]4.6%36
- Lameness2.6%20
- Ineffective, estrus synchroniz[legacy FDA term: the product did not have the expected effect (estrus synchroniz)]2.4%19
- Death by euthanasia[the animal was euthanized]2.1%16
- Pneumonia[lung infection or inflammation]1.9%15
- Unclassifiable adverse event[event that fits no dictionary term]1.4%11
- Found dead1.3%10
- Rectal prolapse1.3%10
- Sexual disorder NOS[NOS: not otherwise specified]1.3%10
- Accidental exposure[exposure that was not intended]1.2%9
- Behavioural disorder NOS[behaviour change, type not specified]1.2%9
- Bloated1.2%9
- Respiratory tract disorder NOS[NOS: not otherwise specified]1%8
- Vaginal prolapse1%8
- Closure, Abnormal[a product quality report, not a sign in an animal]0.9%7
- Infertility NOS[NOS: not otherwise specified]0.8%6
- Digestive tract disorder NOS[digestive problem, type not specified]0.6%5
- Necropsy performed0.6%5
- Respiratory tract infection NOS[NOS: not otherwise specified]0.6%5
- Seal, Abnormal[a product quality report, not a sign in an animal]0.6%5
- Underdose[less than the labelled amount was given]0.6%5
- Underfilling, Container[a product quality report, not a sign in an animal]0.6%5
- Abnormal oestrus NOS[NOS: not otherwise specified]0.5%4
- Acute (interstitial) pneumonia/pleuropneumonia0.5%4
Top 30 of 149 coded terms (VeDDRA, the veterinary reporting dictionary; plain-language gloss in brackets). One report can list several terms. The ticks show how often the same term appears in a wider pool of reports; they describe the reports, and FDA cautions that such figures cannot be used to estimate risk or to compare one product with another. openFDA masks brand and manufacturer names in adverse event records, so the reports counted here cannot be attributed to a particular brand.
Outcomes and report types
Outcome recorded in the report
What kind of report it was
Coloured bar: reports naming melengestrol acetate. Grey bar: all 1,357,245 reports in the database. Outcomes are the status at the time of the last report, as stated by the reporter; a report covering several animals can carry more than one outcome. FDA has not necessarily determined whether any drug played a part in any outcome.
Species and breeds in the reports
Single-breed animals
Breed shares follow how common each breed is. Crossbred animals and reports with no breed stay in the species figure only.
Age, weight and route
Age of the animal
Weight of the animal
Route of administration stated in reports: oral (726).
In context
| Measure | Melengestrol Acetate | All cattle reports | All reports |
|---|---|---|---|
| Reports | 776 | 31,229 | 1,357,245 |
| Share of that pool's reports naming this drug | — | 2.4% | 0.1% |
| Classed serious, of reports stating it | 22.3% | 58.4% | 38.6% |
| Death or euthanasia recorded, per 1,000 reports | 108.2 | 368 | 63.8 |
| Filed as lack of expected effectiveness (wholly or partly) | 25.6% | — | 23% |
| Top term, share of reports | Ineffective, estrus suppressio 66.9% | 1.7% | — |
This set accounts for 98.2% of all reports naming melengestrol acetate, so no separate ingredient column is shown. Shares are of reports, not of animals treated. The number of doses sold is not public, so none of these figures is a rate of occurrence, and differences between columns reflect which animals receive a drug and who reports as much as anything else.
FDA-approved products containing melengestrol acetate (Green Book)
Reference information, not report statistics. openFDA masks brand and manufacturer names in adverse event records, so the reports counted here cannot be attributed to a particular brand. The list below is the FDA Green Book as of 30 Sep 2026; nothing on this page says which of these products, if any, a report concerned.
| Trade name | Active ingredients | Sponsor | Approved for | Application |
|---|---|---|---|---|
| MGA 100; MGA 200 | Melengestrol Acetate | Phibro Animal Health Corp. | Cattle | NADA 034-254 |
| MGA 100; MGA 200; MGA 500 | Melengestrol Acetate | Phibro Animal Health Corp. | Cattle | NADA 039-402 |
| HeifermaX 500 | Melengestrol Acetate | Elanco US Inc. | Cattle | ANADA 200-343 |
| CycleGuard 500 | Melengestrol Acetate | Huvepharma EOOD | Cattle | ANADA 200-399 |
| MEL 500 | Melengestrol Acetate | Virbac AH, Inc. | Cattle | ANADA 200-805 |
Species are the major species the Green Book search lists for the application ("—" where it lists another species or none). Approval dates are not part of the Green Book listing files and are not shown. Pioneer applications (NADA) come first, then generics (ANADA).
Questions about melengestrol acetate reports
How many adverse event reports has FDA received for melengestrol acetate?
776 reports record a drug with melengestrol acetate as its active ingredient in the openFDA release of 28 Sep 2026, covering reports received through March 2026. 13 of them arrived in the latest 12 months.
Which brand do these reports concern?
That cannot be known from the public data. openFDA masks brand and manufacturer names in adverse event records, so the reports counted here cannot be attributed to a particular brand. The Green Book lists 5 approved applications with this ingredient alone; the reference list on this page names them without any counts.
What signs are reported most often?
ineffective, estrus suppressio (66.9%), inappropriate preparation of medication (12%), lack of efficacy - NOS (10.7%), death (6.4%) and no sign (4.6%). These are the coded terms listed in reports; several can appear in one report, and a term's presence is not a finding that the drug was responsible.
Which species and breeds appear in these reports?
cattle (95.9%), sheep (0.3%) and human exposure (0.1%). Among single-breed animals the most frequent labels are Aberdeen Angus, Holstein-Friesian, British White and Charolais; popular breeds appear often in any drug's reports because there are more of them.
Are reports rising?
13 reports in the 12 months to March 2026, down 32% from 19 in the 12 months before. FDA posts reports quarterly with a delay of three to six months, so the newest months are incomplete and usually grow in later releases. Counts also move with sales, publicity and time on the market.
Do these reports show that melengestrol acetate harms pets?
Report counts cannot show that. FDA states that "there is no certainty that the reported drug or device caused the adverse event" and that the event "may have been related to an underlying disease, other drugs used at the same time or other non-drug related sources." FDA also notes that commonly used products may have more reports simply because more animals receive them.
Are these the side effects of melengestrol acetate?
They are signs listed in reports, not an established list of side effects. The adverse reactions observed in studies are printed on each product's FDA-approved label, which a veterinarian can go through with you. This page is a record of what was reported to FDA.
How do I report a problem with an animal drug?
FDA asks owners and veterinarians to call the drug company first (the number is on the label); companies must pass reports to FDA. Reports can also go directly to FDA on Form FDA 1932a. See the guide on how to report.
Where this comes from. Counts are built from the openFDA Animal & Veterinary adverse event bulk files released 28 Sep 2026, which hold reports FDA's Center for Veterinary Medicine received through 31 Mar 2026. openFDA masks brand and manufacturer names in these files, so drugs are counted by the active ingredients each record discloses and no figure is attributed to a brand, application or company. Ingredient names, and the separate reference lists of approved products, follow the FDA Green Book as of 30 Sep 2026. Drug entries are grouped by the active ingredients their unmasked ingredient field discloses; the application number that records also carry is not used. No report text, lot numbers or reporter details are published. See the methodology and sources; FDA's record is authoritative, and corrections are handled within five working days.