The effects of whitening can last for several months, but may vary depending on the lifestyle of the patient. Factors that decrease whitening include smoking and the ingestion of dark colored liquids like coffee, tea and red wine. Whitening treatment though can be repeated and especially for at-home whitening with gel, patient can buy extra whitening gel from the practice and use it with the customised whitening trays. A new prescription from the dentist is not necessary.