1 What is this medicine
and what is it used for?
Megestrol acetate is a synthetic derivative of progesterone
(progestogen) with multiple clinical applications. At high doses (160 mg), it
stimulates appetite and promotes weight gain through central and peripheral
mechanisms including stimulation of neuropeptide Y in the hypothalamus,
reduction of pro-inflammatory cytokines (IL-1, IL-6, TNF-alpha), and possibly
direct anabolic effects.
Megace 160 mg tablets are used for:
• Anorexia-cachexia syndrome — appetite
stimulation and weight gain in patients with AIDS-associated anorexia/weight
loss or cancer-associated cachexia.
• Palliative hormonal therapy —
advanced breast cancer (second-line after tamoxifen) and advanced endometrial
carcinoma.
2 How to take this
medicine
For anorexia/cachexia: 400–800 mg once daily (2.5–5 tablets).
For hormonal cancer therapy: 160 mg once daily (1 tablet) for breast cancer;
40–320 mg/day in divided doses for endometrial cancer. Take with or without
food. Swallow whole with water.
|
Take at the same time each day. Clinical response (improved appetite and weight
gain) may take 4–8 weeks — continue treatment for at least 8 weeks before
assessing efficacy. This medicine does not treat the underlying
cause of weight loss — it works alongside nutritional support. |
3 Possible side effects
|
Frequency |
Side Effect |
What to Do |
|
Very Common (>10%) |
Weight gain / fluid
retention |
Monitor weight;
dietary advice to ensure quality weight gain rather than just fat/fluid
accumulation. |
|
Very Common (>10%) |
Deep vein thrombosis
(DVT) / thromboembolism |
High risk — see
warning. Assess VTE risk before prescribing. |
|
Common (1–10%) |
Hypertension |
Monitor blood
pressure. |
|
Common (1–10%) |
Impotence / decreased
libido (males) |
Counsel patient; usual
response to progestogen therapy. |
|
Common (1–10%) |
Hyperglycaemia /
exacerbation of diabetes |
Monitor blood sugar —
progestogens can worsen glycaemic control. |
|
Common (1–10%) |
Adrenal insufficiency
(with long-term use) |
Megestrol suppresses
the HPA axis — risk of adrenal crisis on sudden withdrawal. |
|
Common (1–10%) |
Mood changes /
depression |
Monitor psychological
wellbeing. |
|
Seek help urgently |
Symptoms of DVT (leg
pain/swelling) or PE (sudden breathlessness, chest pain) |
Seek emergency medical
attention. |
|
THROMBOEMBOLIC RISK: Megestrol acetate significantly increases the
risk of venous thromboembolism (DVT and pulmonary embolism). Risk factors: immobility, cancer, prior VTE,
obesity, elderly age, combined oestrogen therapy. Consider thromboprophylaxis in high-risk
patients. Monitor for signs of clot during treatment. ADRENAL SUPPRESSION: Long-term megestrol
suppresses the hypothalamic-pituitary-adrenal (HPA) axis. Do not stop
suddenly after prolonged use — gradual taper required. Stress dosing may be
needed perioperatively. |
||
4 Contraindications
Megestrol is contraindicated in: known or suspected pregnancy
(teratogenic); active thromboembolic disease; known hypersensitivity; and as a
diagnostic test for pregnancy. Use with extreme caution in: diabetes;
cardiovascular disease; history of VTE; and renal impairment.
5 Drug interactions
• Anticoagulants (warfarin): megestrol
can alter INR — monitor closely.
• Insulin / oral hypoglycaemics:
megestrol causes hyperglycaemia — increase monitoring and adjust doses.
• Immunosuppressants (ciclosporin,
tacrolimus): megestrol may increase levels via CYP3A4 inhibition — monitor
levels.
6 Storage
Store below 25°C. Original blister packaging. Keep out of
reach of children.
7 Prescription
requirement
|
PRESCRIPTION ONLY MEDICINE (POM) — GP or
oncology/palliative care specialist prescription. Monitoring: weight, blood glucose, blood
pressure, signs of VTE. |
8 Guidance for patients
& caregivers
Megestrol works by stimulating appetite and reducing the
inflammatory processes that cause cancer or AIDS-related weight loss. It is
most effective when combined with regular nutritional support — eating small, frequent meals, fortified foods, and nutritional supplements alongside the
medicine gives the best results.
The most important risk is blood clots. If you develop pain
or swelling in one leg, or sudden shortness of breath, seek emergency medical
help immediately.
Do not stop this medicine suddenly after long-term use —
adrenal suppression means your body needs to gradually readjust its hormone
production. Always taper under your doctor's guidance.
9 Pharmacist &
prescriber notes
Megestrol acetate 160 mg tablets are used at 400–800 mg/day
for cachexia (2.5–5 tablets). The 30-tablet pack covers one month at 160 mg/day
(hormonal) or 10 days at 400 mg/day (cachexia — would need multiple packs).
Adrenal suppression: megestrol is a potent glucocorticoid
agonist as well as progestogen — long-term use (>6 weeks) at doses ≥ 160
mg/day suppresses the HPA axis similarly to prednisolone. Taper slowly;
perioperative stress dosing with hydrocortisone may be required.
New-onset diabetes or worsening glycaemic control is very
common — check HbA1c at baseline. The weight gain seen with megestrol is
primarily adipose tissue and fluid, not lean muscle mass — nutritional support
is still required for functional improvement.
10 Frequently asked
questions
I was told this medicine can cause blood clots — how
worried should I be?
The risk is real, particularly in patients who are also
dealing with cancer, immobility, or obesity. Signs of a blood clot include:
one-sided leg pain or swelling, sudden shortness of breath, or chest pain.
Contact emergency services immediately if you develop these symptoms.
Can I stop this medicine suddenly?
Not if you have been taking it for more than a few weeks at
higher doses. Long-term megestrol suppresses adrenal gland function, and
stopping suddenly can cause adrenal crisis (extreme fatigue, weakness, low
blood pressure). Always reduce the dose gradually under your doctor's guidance.
Does this medicine treat my cancer?
At the 160 mg dose for breast or endometrial cancer, yes — it
has hormonal anti-cancer activity. For cachexia/appetite stimulation, it treats
the symptom of weight loss but does not treat the underlying cancer.
Can it affect my blood sugar?
Yes — megestrol can raise blood sugar levels, which is
particularly important for diabetic patients. Blood glucose monitoring should
be increased when starting this medicine.
Is megestrol suitable for children?
Megestrol is not routinely used in children. Paediatric use
requires specialist supervision.