**Background:** Oral discomfort—including mucositis, xerostomia, dysgeusia, and loss of appetite—is a common and debilitating side effect of head-neck cancer treatment. Many cancer patients use complementary and alternative medicine, including herbal products, to alleviate these symptoms, but physicians often feel ill-equipped to counsel patients due to lack of knowledge. The German National Guidelines on Supportive Care and on Complementary and Alternative Medicine mention only chamomile and aloe vera for oral mucositis, citing insufficient evidence. This study aimed to assess the knowledge and usage patterns of medicinal plants among head-neck cancer patients and medical students, and to compare practiced knowledge with written folk medicine.
**Methods:** The authors screened ten German books on phytotherapy (including layman's, specialist's, and plant identification books) for plants recommended for treating oral mucositis, xerostomia, and loss of appetite. A numerical scoring system was used to generate a 'hit list' of the most frequently recommended plants. From this, a simple questionnaire was developed covering 16 plants. Between August and September 2020, 120 head-neck cancer patients were recruited from the out-patient clinic of the Department of Otolaryngology and Head Neck Surgery (Südharz Hospital, Nordhausen, Germany). All had undergone chemotherapy and/or local radiation. Between March and April 2020, 168 medical students (151 human medicine, 1 dental medicine, 10 other, 6 no information) were recruited via social media and surveyed using the same questionnaire via an online tool (soscisurvey.de). Students were additionally asked to write down the indications for which they used each plant. Knowledge and usage rates were calculated as proportions. Median and interquartile range described the number of plants known and used. Groups were compared using an unpaired Student's t-test (p < 0.05 considered significant). Heat-map cluster analysis, principal component analysis (PCA), VENN diagrams, and network analysis were used for visualization.
**Key Results:** Head-neck cancer patients knew a median of 8 [IQR 5.25–11.0] plants. The five most commonly known plants were Matricaria recutita L. (96.7%), Zingiber officinale ROSCOE (92.5%), Salvia officinalis L. (91.7%), Taraxacum Wigg. (83.3%), and Calendula officinalis L. (73.3%). The user rate among patients was 82.50%, with a median of 3.0 [IQR 1.0–4.0] plants used. The most used plants were Matricaria recutita L. (70.0%), Salvia officinalis L. (57.5%), Zingiber officinale ROSCOE (46.7%), Carum carvi/Cuminum cyminum L. (25.0%), and Calendula officinalis L. (24.2%). Medical students knew a median of 8 [IQR 6.0–10.5] plants. The most commonly known plants were Taraxacum Wigg. (82.4%), Carum carvi/Cuminum cyminum L. (75.8%), Calendula officinalis L. (73.8%), Zingiber officinale ROSCOE (72.1%), and Matricaria recutita L. (70.9%). The user rate among students was 93.94%, with a median of 4.0 [IQR 2.0–5.0] plants used. The most used plants were Zingiber officinale ROSCOE (78.8%), Matricaria recutita L. (78.2%), Salvia officinalis L. (66.7%), Carum carvi/Cuminum cyminum L. (38.8%), and Calendula officinalis L. (26.1%). While the number of plants known did not differ significantly between groups, students used significantly more plants in daily life (p < 0.001, t = 3.436, Student's t-test). The top five most commonly used plants were identical between groups. PCA and heat-map analysis showed that overall knowledge and usage patterns were similar, though patients showed a preference for Matricaria recutita L. and Salvia officinalis L. (plants recommended for oral mucositis), while students were more familiar with Cetraria islandica L. and Carum carvi/Cuminum cyminum L. Comparison of students' stated indications with literature indications revealed several discrepancies. For example, students associated Zingiber officinale ROSCOE with boosting the immune system—an indication not found in the screened literature—while many literature indications (e.g., using Matricaria recutita L. for menstrual cramps, or Plantago lanceolata L. and Salvia officinalis L. for oral mucositis) were not widely known to students. VENN diagram analysis of the five most used plants showed that literature attributed a common indication of 'abdominal discomfort' to all five, whereas students attributed a common indication of 'common cold' to four of them. Network analysis of student responses revealed three main symptom clusters: plants for abdominal discomfort, plants for oral discomfort, and plants for coughing.
**Clinical Implications:** The user rate of phytotherapy among head-neck cancer patients (82.5%) is substantially higher than previously reported rates (19.7–38%), suggesting that use is often underreported or not communicated to clinicians. The study identifies a condensed canon of five plants—Calendula officinalis L., Carum carvi/Cuminum cyminum L., Matricaria recutita L., Salvia officinalis L., and Zingiber officinale ROSCOE—that are commonly known and used by both patients and future physicians. For four of these five plants, some clinical evidence exists for treating oral discomfort. This small, shared knowledge base could simplify clinical counseling and interaction checking. However, the finding that medical students' knowledge is based more on 'lived' folk medicine than on evidence-based or officially mandated indications raises concerns about the quality of future counseling. The study demonstrates that bioinformatics tools (PCA, heatmaps, VENN diagrams, network analysis) can effectively visualize and compare knowledge across stakeholder groups and knowledge sources. Limitations include potential bias from restricting literature screening to German-language books, possible underestimation of plant recognition due to regional naming variations, and the single-center recruitment of patients.