The agent proven to be effective for teeth whitening is hydrogen peroxide. Only clinics are allowed to prescribe hydrogen peroxide at the concentration which can effectively whiten teeth in a short time.
This is what the Ministry of Health (MOH) has to say about teeth whitening products available over the counter (taken from the MOH website):
" Under the Health Products (Cosmetic Products-ASEAN Cosmetic Directive) Regulations 2007, as long as the concentration of hydrogen peroxide or other similar chemicals present in a finished oral hygiene product is less than or equal to 0.1%, it will be allowed for sale to the public. Regardless of the efficacy of the treatment, no act or legislation has been violated provided the whitening products used by these non-dental professionals contain less than or equal to 0.1% hydrogen peroxide.
MOH will continue to monitor and review this. The dental profession should continue to educate their patients and remind the public that tooth whitening or bleaching should only be done by trained dentists."
