Introduction
Viola odorata is a member of the Violaceae family, which is known by different names such as Bānāfsāj, Sweet Violet, Common Viola, and Garden Violet. This type of plant with many therapeutic properties and less side effects, has been used since the distant past. In traditional Iranian medicine (TIM), it has a cold and moist temperament. Various compounds with multiple clinical and therapeutic effects have been prepared from this plant, which are mainly used for the treatment of cancer, skin, digestive, respiratory, and urinary system diseases. Violet oil also has a cold and moist temperament with effects similar to violet itself. One of its main uses is in skin application for treatment of itching, hives, burns and inflammatory conditions. Considering the low side effects and the many beneficial effects of violet, this review study aims to investigate the pharmacological compounds and therapeutic effects of Viola odorata from the perspective of TIM. 
Methods
In this review study, a search was conducted for the materials in many TIM books such as Canon of Medicine by Ibn Sina, Tuhfat al-Momenin by Hakim Seyyed Mohammad Momenin, al-Jami’ li-Mufradat al-Adwiya wa’l-Aghdhiya by Ibn Baytar, Al-shamel fi al-Sanaat Al-Tabiat by Ibn Nafis, Makhzan al-Adawiyah by Mohammad Hossein Aghili Shirazi, Firdaws al-Hikmah fi al-Tibb by Ali ibn Sahl al-Tabari, Al-Hawi fi al-Tibb by Zakaria Razi, Khulasat al-Hikmah by Mohammad Hossein Aghili Shirazi, as well as the book “PDR for Herbal Medicines”, and for the related studies in online databases such as PubMed and Scopus using the keywords sweet violet, common viola, garden violet, Herbal Medicine, Traditional Iranian Medicine.
Results
In the book Makhzan al-Adawiyah, it has been stated that the temperament (nature) of Viola odorata is firstly cold and secondly moist, or with a reversed order. In Iran, it has been reported in Golestan, Mazandaran, Gilan, West Azarbaijan, Markazi, and Semnan provinces. 
According to studies in modern medicine, viola odorata has various constituents including volatile oils (including salicylic acid, methyl ester and beta-nitropropionic acid), glycosides, tannins, flavonoids, saponins, alkaloids, mucilage, gallates, phenols, vitamin C and coumarin. In addition, Sitosterol (a plant sterol similar to the synthetic analogs of hydrocortisone and corticosteroids) is present in various plants, including Viola odorata.
Viola odorata is used in different forms including violet oil (for topical use or in the form of nasal drops for the treatment of nervous and skin disorders) and in the form of tablets, extracts, syrups, concoctions, or semi-solid oral forms for skin, respiratory, digestive, and urinary system and sleep disorders. All parts of the plant are used as medicine. In TIM, it is used for various therapeutic purposes.
The plant should not be boiled too much, because its effect will be reduced; it is always better to brew it. It is usually eaten with brown sugar; if it is eaten with plums, jujubes, tamarind, fumaria officinalis, and myrobalan, it can be used as a strong laxative. When combining viola odorata with other medicines, it should be taken into account that the strength of one does not nullify the strength of the other. Its cooked form is better for the stomach and it can be digested faster. An important thing to keep in mind for the positive effect of the plant is that the dried plant should not be old.
Several studies have been conducted on the viola odorata and its effects on the pulmonary, digestive and nervous systems (sedation, pain relief and sleep) as well as anti-inflammatory and antioxidant effects, anti-tumoral, anti-obesity and anti-hypertensive, antibacterial and antifungal, anti-febrile and diuretic effects have been reported. 
No harmful and dangerous side effects have been reported from the correct consumption of the plant’s flowers, rhizomes, and oil or the whole plant in modern medicine studies, but in the TIM books, it has been pointed out that excessive consumption of viola odorata causes weakness of the heart, discomfort and heaviness of the stomach, and nausea, and smelling it may cause a cold. Some scholars considered these harms to be specific to the dry form of viola odorata. Recommendations have been provided to solve these complications. For example, some recommended the use of anise in low dose, and some recommended the use of wallflower (Cheiranthus cheiri) and marjoram to cure the cold caused by smelling the plant. Viola odorata’s alternative is lotus or malva leaves and to treat coughs, borage and licorice root can be used.
Discussion
According to the sources and practices of scholars in TIM sages as well as the studies conducted in the field of modern medicine, the viola odorata plant has many systemic or local therapeutic applications without having any serious or special side effects. Considering that some of the beneficial effects of this plant have not yet been proven in modern medicine, it is recommended to conduct more clinical and experimental studies to prove its other therapeutic effects. In addition, due to the availability of this plant in many countries, it is recommended to make different medicinal products from this plant and make it available to patients or be used as a complementary medicine along with other common treatments.

Ethical Considerations
Compliance with ethical guidelines
This study was approved by the ethics committee of Mashhad University of Medical Sciences (Code: R.MUMS.REC.1396.174 ).

Funding
This study was extracted from a thesis (No. 960434) and funded by Mashhad University of Medical Sciences.

Authors' contributions
All authors equally contributed to preparing this article.

Conflicts of interest
The authors declared no conflict of interest.

Acknowledgements
The authors would like to thank the Vice-Chancellor for research of Mashhad University of Medical Sciences for their support.


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