People with pre-existing health conditions should be careful when taking stimulant drinks, such as Red Bull or 5-Hour Energy shots.
They often contain caffeine, which can be risky for people with heart problems, for example.
"The stimulants can potentially worsen anxiety in anxious patients," pointed out Dr Derek Koh, who heads Thomson Wellth Clinic @ Novena.
"They may not be good for patients with underlying heart diseases, as they would cause palpitations."
When it comes to buying off-the-shelf supplements, senior pharmacist Serena Kon advises caution, as these products are not regulated by the Health Sciences Authority.
"Individuals need to be mindful to purchase their supplements from trusted sources and be vigilant in evaluating claims made by supplement vendors," said Ms Kon, who works at the Singapore General Hospital.
As a general rule, many factors affect how long it takes for a supplement's benefits to kick in, added Ms Kon.
In one research paper published in 2005, scientists studied people taking 1,500mg of oral glucosamine every day. The supplement is supposed to help with joint health.
They found that it took at least two weeks to reduce joint pain and increase a person's mobility.
Said Ms Kon: "Patients have to be aware that very few natural supplements have been vigorously studied in clinical trials, and that evidence for the use of natural supplements is not as robust compared to prescription medicines."
Added Dr Derek Li, a family physician at Raffles Medical: "In many cases, we may never see any difference as we are not deficient in anything."
While most reputable supplements are "very safe" for consumption, Dr Li said, those with chronic health problems or allergies should pay extra attention to what they are eating.
"A good example is glucosamine... which is usually derived from shellfish products," he said. "Therefore, people with shellfish allergies should avoid such supplements."
If a healthy person plans his meals carefully and gets regular exercise, he might not need supplements at all, said Dr Li.
He added that one possible exception could be vitamin D, which is normally obtained through exposure to sunlight.
"One might expect that this should not be a problem living in Singapore," he said.
"But I have come across patients who see very little sunshine due to the nature of their jobs, and hence develop vitamin D insufficiency over time."