At 47kg, Gillian (not her real name) was healthy but haunted by the image of herself as an overweight teenager. She wanted to be 45kg.

The 24-year-old, who is 1.6m tall, turned to Malaysian slimming drink Bello Smaze, which had pages of glowing testimonials on Facebook.

But within four days of consuming it, she developed palpitations, insomnia and subsequently suicidal thoughts. She stopped taking it immediately.

"On my first day, I broke out in a cold sweat a few hours after drinking it. I don't suffer from depression but suddenly, I had suicidal thoughts and was overwhelmed by my past of being bullied for my size," she said.

Gillian told The Straits Times she was swayed by the many success stories she read online. "The seller even sent me a certificate in Malay that she said is from the Malaysian authorities stating Bello Smaze is safe."

But tests by the Health Sciences Authority (HSA) here found it has a banned weight-loss substance.

Called sibutramine, it can cause mood swings, hallucinations, heart attacks and strokes, said Associate Professor Chan Cheng Leng, group director of the health products regulation group at HSA.

Bello Smaze is among four health products the HSA yesterday alerted people to after five consumers reported adverse reactions to them, including one woman who now has severe heart failure.

Its statement said three of the products are for weight loss: BB Body, Bello Smaze and Choco Fit. The fourth is Seahorse Chop Du Zhong Ba Ji Wan, which has a potent steroid called dexamethasone.

In one of the more severe cases, a woman in her 50s, who had bought BB Body from an online seller in Malaysia, now suffers from severe heart failure.

Cardiologist Lee Chee Wan, who treated her, told The Straits Times yesterday that the woman has had a defibrillator implanted to regulate her heart rhythm as her heart is likely to fail again within a year.

She also requires long-term heart failure medication.

Her case is one of the worst Dr Lee said he has heard of.

"Most slimming products don't work or are unsafe. Even if you do check the ingredient list, some products do not declare they contain harmful substances," he added.

In a separate case, a woman in her 30s had palpitations after consuming Choco Fit for two days.

The HSA said their adverse reactions were consistent with the effects of sibutramine, which it banned in 2010 due to an increased risk of heart attacks, strokes and other serious side effects.

BB Body, Bello Smaze and Choco Fit were marketed on various e-commerce and social media platforms, such as Instagram and Facebook, as having "no side effects" or being able to deliver weight loss in days.

HSA said it has directed administrators of the local online platforms to remove the product listings.

Elaborating later, it told The Straits Times it monitors local websites and e-commerce platforms which sell medicines or suspected illegal health products.

It also works closely with overseas regulatory agencies and Interpol for information sharing on illegal health products.

But experts say it is difficult to regulate online transactions of drugs, with the rise in online shopping.

Professor William Chen, director of Nanyang Technological University's food science and technology programme, said: "While our HSA has put in place robust inspection procedures for health products and ingredients, it may not be practical to implement such inspections on products purchased online and from overseas sources."

HSA's Prof Chan also urged people to be wary of claims or promises of quick weight loss.

Her agency's enforcement operations show many weight-loss products sold on e-commerce platforms without an established retail presence contain sibutramine, she said.

HSA also warned against Seahorse Chop Du Zhong Ba Ji Wan, which led to Cushing's syndrome in a man in his 40s. He had bought the product from a medical hall in Johor Baru and took it for more than two months to relieve his arthritis.

The HSA found blister strips in one of the boxes carrying a different product name and labelled as "100% Natural Pure Herbal *Acti Fast", which it pointed out was another sign the product was illegal.

HSA advised sellers and suppliers to stop selling the four products immediately. Anyone convicted of selling them may be jailed for up to three years or fined up to $100,000.

Meanwhile, Gillian said the side effects subsided a week after she stopped taking Bello Smaze.

"I won't be taking these kinds of products any more and will stick to exercising," she said.

HSA's advice to consumers

• Stop taking Bello Smaze, BB Body or Choco Fit immediately and consult a doctor if you feel unwell or are concerned about your health.

• See a doctor as soon as possible if you have taken or are taking Seahorse Chop Du Zhong Ba Ji Wan because it contains a potent steroid. Discontinuing the consumption of steroids without medical supervision can cause serious withdrawal symptoms such as fatigue, confusion and low blood pressure, especially when the product has been taken for more than a few weeks.

• Be wary of health products that promise or deliver quick and miraculous effects, or carry exaggerated claims.

• Avoid buying health products from unfamiliar sources overseas, and be careful when buying them online. You cannot be sure where and how these products were made. They could be counterfeit or have undeclared ingredients which can seriously harm your health.