Participants in the control group will receive the placebo intervention in addition to standard care. Participants will be provided with an identical aromatherapy inhaler stick infused solely with jojoba oil. Jojoba oil, primarily used as a carrier oil for dilution, has little to- no scent and no known therapeutic or anxiolytic effects when inhaled. This ensures that any potential benefits observed in the intervention group can be attributed to the active essential oil blends rather than the inhalation process itself.

Participants in the intervention group will receive inhalation therapy via an aromatherapy inhaler stick*, on top of standard care.

Participants will be instructed to use the inhaler stick every four hours when they are awake, and whenever they feel nauseous, by holding the inhaler stick a finger's length away from their nostrils and inhaling through one nostril at a time. Each administration should not last more than 5 minutes. Participants will commence using the inhaler stick on the day of chemotherapy, until five days after the completion of chemotherapy (a total of six days).

Participants in the intervention group will receive inhalation therapy via an aromatherapy inhaler stick*, on top of standard care. Participants will be instructed to use the inhaler stick every four hours when they are awake, and whenever they feel nauseous, by holding the inhaler stick a finger's length away from their nostrils and inhaling through one nostril at a time. Each inhaler administration should not last more than 5 minutes. Participants will commence using the inhaler stick on the day of chemotherapy, until five days after the completion of chemotherapy (total of six days). Given the subjective nature of scents, participants in the intervention group will be given a choice between two therapeutic aroma blends - N1 and N2 - before commencing the study. This approach aims to minimize the risk of negative associations with a particular scent and enhance participant adherence to the intervention.

Percentage of eligible patients who consent to join the study will be measured to evaluate the feasibility of using inhalation aromatherapy to reduce chemotherapy-induced nausea and vomiting (CINV) for patients undergoing haematopoietic stem cell transplant (HSCT)

Percentage of participants who complete the study will be measured to evaluate the feasibility of using inhalation aromatherapy to reduce chemotherapy-induced nausea and vomiting (CINV) for patients undergoing haematopoietic stem cell transplant (HSCT)

Percentage of participants in the intervention group who use the inhaler stick as instructed measured to evaluate the feasibility of using inhalation aromatherapy to reduce chemotherapy-induced nausea and vomiting (CINV) for patients undergoing haematopoietic stem cell transplant (HSCT)

Measured through Likert-scale items at the end of the study to evaluate the acceptability of using inhalation aromatherapy to reduce chemotherapy-induced nausea and vomiting (CINV) for patients undergoing hematopoietic stem cell transplant (HSCT). The Feasibility of intervention Likert-scale and the Acceptability of intervention Liker-scale will be used. The Likert-scale consist of a rating of 1- 5 where 1 is strongly disagree and 5 is strongly agree and to be rated by participants.

Qualitative insights from semi-structured interviews on ease of use, perceived helpfulness and overall experience to evaluate acceptability of using inhalation aromatherapy to reduce chemotherapy-induced nausea and vomiting (CINV) for patients undergoing haematopoietic stem cell transplant (HSCT)

Patient-reported nausea severity measured daily using a Visual Analog Scale (VAS, 0 = no nausea, 10 = worst possible nausea).