SINGAPORE - Drinking a local brand of "organic orange juice" could give you a heart attack, stroke, loss of hearing or vision because it contains strong medicine used to treat erectile dysfunction, the Health Sciences Authority (HSA) warned on Friday.

It found "undeclared potent chemical ingredients" in four S Lion Juice products which are sold online.

One of them, S Lion Juice 10 gm, contains tadalafil, the active ingredient in Cialis - a prescription drug used to treat male erectile dysfunction.

The other three drinks had chemically related compounds of this drug or sildenafil which is sold as Viagra.

The HSA said: "These products carried claims such as 'increase energy and stamina', 'improve sleep quality', 'improve brain functionality', 'strengthen bones, prevent osteoporosis', and 'help menopausal women regain their emotional health and strength'."

However, tests found they contained various medication for male erectile dysfunction.

These medicines, it said, are "not suitable for women and certain men, including those under 18 years of age, and patients with heart-related problems or who are on heart medications such as nitrates".

There have been reports in other countries of deaths in men who take such drugs while also taking nitrates to treat heart problems.

The HSA urges anyone who has bought these juices to stop taking them immediately and to see a doctor if they do not feel well.

It added: "HSA is currently investigating the sellers of these illegal products and will take strong enforcement actions against individuals who engage in the sale and supply of health products containing undeclared medicinal ingredients."

The company claims on its website that it makes all its products "based on intensive research, consultation with experts, testing and proven results", adding: "All our products are manufactured, tested and certified in Singapore."

The HSA has issued a warning for consumers to be wary when purchasing health products from dubious online sites. It said: " When buying health products online, only buy them from websites with an established retail presence in Singapore."