Purpose To update the clinical practice guidelines for the use of natural and miscellaneous agents for the prevention and/or treatment of oral mucositis (OM). Methods A systematic review was conducted by the Mucositis Study Group of the Multinational Association of Supportive Care in Cancer / International Society of Oral Oncology (MASCC/ISOO). The body of evidence for each intervention, in each cancer treatment setting, was assigned an evidence level. The findings were added to the database used to develop the 2014 MASCC/ISOO clinical practice guidelines. Based on the evidence level, the following guidelines were determined: Recommendation, Suggestion, and No Guideline Possible. Results A total of 78 papers were identified within the scope of this section, out of which 29 were included in this part, and were analyzed with 27 previously reviewed studies. A new Suggestion was made for oral glutamine for the prevention of OM in head and neck (H&N) cancer patients receiving radiotherapy with concomitant chemotherapy. The previous Recommendation against the use of parenteral glutamine for the prevention of OM in hematopoietic stem cell transplantation (HSCT) patients was re-established. A previous Suggestion for zinc to prevent OM in H&N cancer patients treated with radiotherapy or chemo-radiotherapy was reversed to No Guideline Possible. No guideline was possible for other interventions. Conclusions Of the vitamins, minerals, and nutritional supplements studied for the management of OM, the evidence supports a Recommendation against parenteral glutamine in HSCT patients and a Suggestion in favor of oral glutamine in H&N cancer patients for the management of OM.