Health chiefs have issued an urgent warning to men suffering from erectile dysfunction -- DON'T reach for dodgy black-market sex pills, as the embarrassing problem could be an early warning sign of killer illnesses lurking beneath the surface.

The Ministry of Health and Sanitation sounded the alarm in a Facebook post on Monday, revealing that ED -- the inability to get or keep an erection firm enough for sex -- is far more common than most blokes realise, and should never be brushed under the carpet.

Health chiefs say the bedroom struggle is often linked to a terrifying list of underlying conditions including high blood pressure, diabetes, heart disease, stress, depression, heavy drinking and smoking.

And it's more widespread than you might think. Sexual health expert Dr Zaziwe Gundah revealed a staggering HALF of men aged 40 to 70 experience some degree of ED worldwide -- with global cases set to rocket to a mind-boggling 322 million.

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Back home, a 2013 study found more than a third of Malawian men -- 36 per cent -- were affected, mostly with mild cases.

But Dr Gundah warned things are getting worse, with a surge in SEVERE cases now being driven by rising diabetes, hypertension, heart disease and clogged arteries.

His message to embarrassed blokes suffering in silence? Don't suffer alone -- and definitely don't self-medicate.

"ED is treatable," Dr Gundah insisted, revealing doctors can get to the bottom of the problem through blood tests, hormone checks and even ultrasound scans to check blood flow.

Treatment options available in Malawi include lifestyle changes, therapy and prescription meds such as sildenafil (the active ingredient in Viagra), tadalafil, vardenafil and avanafil -- but docs stress these must ONLY be taken under medical supervision, not bought off the back of a lorry.