# Megestrol Acetate: veterinary dose and monograph

> Megestrol Acetate is a veterinary drug. A synthetic oral PROGESTIN historically used to postpone/suppress oestrus and treat false pregnancy in dogs, and (off-label) for a range of feline problems — behavioural issues (urine marking, aggression), miliary dermatitis/eosinophilic… Indications include postponement / suppression of oestrus in the bitch (short-term); false (pseudo) pregnancy in dogs; feline behavioural problems (urine marking, aggression) — off-label, when behaviour modification/other drugs fail. This monograph lists 6 reference doses for dogs, cats and horses, each with route, frequency and source.

Source: https://vetmasterji.com/drugs/megestrol-acetate · Last reviewed: 2026-10-01

## At a glance

- **Drug class:** Veterinary drug
- **Also known as:** Ovaban, Megace, MA
- **Species with doses:** Dogs, Cats and Horses
- **General dose range:** 0.5–2 mg/kg PO q24h (then taper) — check the species tables for the indication
- **Routes:** PO
- **Last reviewed:** 1 October 2026

## Indications

- Postponement / suppression of oestrus in the bitch (short-term)
- False (pseudo) pregnancy in dogs
- Feline behavioural problems (urine marking, aggression) — off-label, when behaviour modification/other drugs fail
- Feline eosinophilic granuloma complex / miliary dermatitis / stomatitis (off-label, refractory)

## Megestrol Acetate dose by species

Doses are per administration unless stated. mg/kg doses scale with body weight; per-animal, per-quarter and infusion-rate doses are shown as the reference writes them.

### Dogs

*Megestrol Acetate doses for dogs*

| Indication | Dose | Route | Frequency | Duration |
| --- | --- | --- | --- | --- |
| Oestrus suppression (start in first 3 days of proestrus) | 2–2.2 mg/kg | PO | q24h | 8 days |
| Oestrus postponement (start in anoestrus) | 0.5–0.55 mg/kg | PO | q24h | 32 days |
| Benign prostatic hypertrophy / pseudocyesis | 0.1–0.55 mg/kg | PO | q24h | BPH 3–8 weeks; pseudocyesis 8 days |

- Oestrus suppression (start in first 3 days of proestrus): Papich 5e: proestrus 2 mg/kg q24h PO for 8 days. Plumb’s p.771: 2.2 mg/kg once daily for 8 days from the first 3 days of proestrus (≈92% efficacy; Woody; Burke). Do not use in the first oestrus or in breeding bitches; do not repeat more often than every 6 months; pyometra and diabetes risk.
- Oestrus postponement (start in anoestrus): Papich 5e: anoestrus 0.5 mg/kg q24h PO for 32 days. Plumb’s p.771: 0.55 mg/kg daily for 32 days starting at least 7 days before proestrus (check vaginal cytology first).
- Benign prostatic hypertrophy / pseudocyesis: Plumb’s p.771: BPH 0.5 mg/kg daily for 4–8 weeks (Root Kustritz) or 0.1–0.5 mg/kg/day for 3–8 weeks before castration (Lane); pseudocyesis 0.5 mg/kg daily for 8 days. BPH 0.55 mg/kg PO daily (Purswell 1999).

### Cats

*Megestrol Acetate doses for cats*

| Indication | Dose | Route | Frequency | Duration |
| --- | --- | --- | --- | --- |
| Refractory dermatologic / behavioural disease (last resort) | 2.5–5 mg/cat | PO | q24–48h for 1–3 weeks, then once weekly | — |
| Oestrus suppression | 2.5–5 mg/cat | PO | 5 mg daily for 3 days, then 2.5–5 mg once weekly | up to 10 weeks |

- Refractory dermatologic / behavioural disease (last resort): Papich 5e: dermatologic therapy or urine spraying 2.5–5 mg per cat q24h for 1 week, then 5 mg once or twice weekly. Plumb’s p.771: atopy 2.5–5 mg every 48 h for 1–3 weeks, then weekly (Rosychuk); miliary dermatitis maintenance no more than 2.5 mg per week. High risk of diabetes mellitus, adrenal suppression and mammary hyperplasia/neoplasia — informed consent.
- Oestrus suppression: Papich 5e: 5 mg/day for 3 days, then 2.5–5 mg once weekly for 10 weeks; 2.5 mg weekly for long-term use (30 weeks). Plumb’s p.771: in anoestrus 2.5 mg weekly for up to 18 months (Woody).

### Horses

*Megestrol Acetate doses for horses*

| Indication | Dose | Route | Frequency | Duration |
| --- | --- | --- | --- | --- |
| Oestrus suppression | 0.5 mg/kg | PO | q24h | — |

- Oestrus suppression: Papich 5e: horses 0.5 mg/kg q24h PO to suppress oestrus.

## Contraindications

Diabetes mellitus (or risk thereof — especially cats), mammary tumours/hyperplasia, uterine disease (pyometra/CEH), pregnancy, and diabetic or unstable patients. Intact females with planned breeding (effects on cycle). Concurrent corticosteroids (additive adrenal suppression). Known hypersensitivity.

## Species-specific warnings

> **Caution:** Cats: High risk of inducing diabetes mellitus (sometimes permanent), mammary fibroadenomatous hyperplasia and adrenal suppression — reserve for refractory cases, lowest dose/shortest course, with glucose monitoring.

## Adverse effects

- Diabetes mellitus (insulin resistance — notably in cats)
- Adrenocortical suppression (iatrogenic hypoadrenocorticism on withdrawal)
- Mammary hyperplasia / mammary neoplasia
- Cystic endometrial hyperplasia–pyometra complex
- Increased appetite/weight gain, lethargy, behavioural change

## Drug interactions

- Corticosteroids: additive adrenal suppression and immunosuppression
- Insulin / oral hypoglycaemics: antagonised glucose control (precipitates/worsens diabetes)
- No major CYP interactions of routine note

## Pregnancy and lactation

Contraindicated in pregnancy (progestin effects on the fetus/pregnancy).

## Monitoring

- Blood glucose (diabetes) — especially in cats and on repeated/prolonged use
- Mammary glands and uterus (hyperplasia/neoplasia, pyometra) — examine before/during use
- Signs of adrenal suppression, particularly on withdrawal
- Body weight/appetite and behaviour

## Toxicity and overdose

Toxicity is the progestin adverse-effect profile rather than acute poisoning: diabetes mellitus (can be permanent, especially cats), iatrogenic adrenal suppression (Addisonian signs on abrupt withdrawal), pyometra, and mammary hyperplasia/neoplasia. These risks — not an LD50 — are why use is limited and short.

Management: No specific antidote. Discontinue and manage consequences: treat diabetes (insulin), provide glucocorticoid support if adrenal suppression/withdrawal signs occur, and address pyometra (ovariohysterectomy) or mammary disease as needed. Supportive care.

## Clinical pearls

- Effective but problematic — modern practice favours safer options first; if used, give the LOWEST dose for the SHORTEST time and obtain informed consent
- Biggest risks: diabetes mellitus (often in cats and sometimes permanent), pyometra, and mammary hyperplasia/neoplasia
- Watch for iatrogenic adrenal suppression — taper rather than stop abruptly after prolonged use
- Screen the mammary glands and uterus before starting, and never use in diabetics or breeding/pregnant animals

## Mechanism of action

A progesterone-receptor agonist that suppresses the hypothalamic–pituitary axis (negative feedback on GnRH/LH/FSH), preventing follicular development and oestrus, and exerts anti-inflammatory/behaviour-modifying progestational effects. The same progestational/glucocorticoid-like activity drives its adverse effects — insulin antagonism (diabetes), adrenal suppression, and uterine/mammary stimulation.

## Formulations and products

- 5 mg tablet (Ovaban)
- 20 mg tablet
- Ovaban (MSD Animal Health) — 5 / 20 mg tablet, Tablet
- Megace — 20 / 40 mg tablet; 40 mg/mL suspension, Tablet / suspension (human-label)

## Storage

Tablets: 15–30 °C, dry, protect from light.

## Before you use this dose

> **Caution:** Reference doses for veterinary professionals. Confirm the dose against the product label, the patient’s condition, current guidance and local regulations before use; the attending veterinarian remains responsible for every clinical decision.

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## Frequently asked questions

### What is the dose of Megestrol Acetate for dogs?

Reference doses for Megestrol Acetate in dogs: 2–2.2 mg/kg PO q24h for 8 days (Oestrus suppression (start in first 3 days of proestrus)); 0.5–0.55 mg/kg PO q24h for 32 days (Oestrus postponement (start in anoestrus)); 0.1–0.55 mg/kg PO q24h for BPH 3–8 weeks; pseudocyesis 8 days (Benign prostatic hypertrophy / pseudocyesis). Confirm against the label and the patient before use.

### What is the dose of Megestrol Acetate for cats?

Reference doses for Megestrol Acetate in cats: 2.5–5 mg/cat PO q24–48h for 1–3 weeks, then once weekly (Refractory dermatologic / behavioural disease (last resort)); 2.5–5 mg/cat PO 5 mg daily for 3 days, then 2.5–5 mg once weekly for up to 10 weeks (Oestrus suppression). Confirm against the label and the patient before use.

### What is the dose of Megestrol Acetate for horses?

Reference doses for Megestrol Acetate in horses: 0.5 mg/kg PO q24h (Oestrus suppression). Confirm against the label and the patient before use.

### When should Megestrol Acetate not be used?

Diabetes mellitus (or risk thereof — especially cats), mammary tumours/hyperplasia, uterine disease (pyometra/CEH), pregnancy, and diabetic or unstable patients. Intact females with planned breeding (effects on cycle). Concurrent corticosteroids (additive adrenal suppression). Known hypersensitivity.

### What are the side effects of Megestrol Acetate in animals?

Diabetes mellitus (insulin resistance — notably in cats); Adrenocortical suppression (iatrogenic hypoadrenocorticism on withdrawal); Mammary hyperplasia / mammary neoplasia; Cystic endometrial hyperplasia–pyometra complex; Increased appetite/weight gain, lethargy, behavioural change.

## Sources

- Plumb's Veterinary Drug Handbook
- Merck Veterinary Manual, 11th edition
- Papich, Papich Handbook of Veterinary Drugs, 5th edition

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VetMasterJi is a clinical decision-support and education platform for veterinary professionals and students. It does not provide veterinary advice, diagnosis or treatment for specific animals. All drug doses, calculators and differentials are references that must be independently verified before clinical use; the attending registered veterinarian remains solely responsible for every clinical decision.