## 1 Introduction  
Presently, diabetes mellitus (DM) is one of the most widely spread diseases [1]. It is a chronic metabolic disorder that results from elevated levels of blood glucose and may be inherited or caused by other lifestyle factors [1]. It is characterized by a defect in the beta cells of the pancreas; consequently, the pancreas either does not produce sufficient amounts of insulin, the utilization of insulin is impaired, or both [1]. In 2019, according to the World Health Organization (WHO) [2], approximately 422 million people worldwide were estimated to have diabetes, and approximately 1.6 million people died of this condition each year. By 2045, this figure is estimated to reach 629 million people globally [3]. Recent studies conducted among different population groups reported prevalence rates of up to 20% in the United Arab Emirates, 16% in Qatar, 24% in SaudiArabia, and 8% in Oman [4]. According to the WHO, the number of people suffering from diabetes in Jordan was 195,000 in 2000, and this number is predicted to increase to 680,000 in 2030 [4]. DM can be classified as type 1 diabetes (T1D), which is characterized by autoimmune damage of the beta cells in the pancreas. Autoimmune destruction usually occurs via autoantibodies mediated by T cells against beta-cell antigens, leading to a decrease in the level of insulin production [1]. The frequency of T1D is reported to range from 5% to 10% of all cases of diabetes [5]. Some environmental factors such as toxins, viral infection, and dietary components can stimulate an autoimmune reaction against beta cells in individuals who are genetically susceptible to T1D. Patients with T1D require exogenous insulin to manage the disease. Type 2 diabetes (T2D) is the result of insulin resistance and impaired beta cell function, which accounts for approximately 90% of all diabetes cases [1; 5; 6]. In the case of insulin resistance, muscles, fat, and liver cells do not respond properly to insulin, resulting in the accumulation of glucose in the bloodstream and a decrease in the amount of glucose entering the cells. This leads to an increase in the production of insulin from the beta cells in the pancreas to compensate for the decreased levels of glucose in the cells [5; 7]. The suggested reasons for insulin resistance include insulin receptor mutation, excess weight, physical inactivity, older age, and smoking [5; 8]. Insulin resistance causes alterations in glucose levels from normal to low (impaired beta cells function) or high (insulin resistance) in patients suffering from T2D. T2D typically occurs in obese individuals and those with a family history of diabetes [5; 9]. Although lifestyle and diet modifications are the basis for the treatment and management of diabetes, most patients will require pharmacotherapy, such as biguanides, sulfonylureas, metformin, and thiazolinediones. Patients with both types of diabetes suffer from polyuria, thirst, blurred vision, and general fatigue [10]. Nevertheless, the use of diabetes medications is usually accompanied by different side effects, including gastrointestinal anomalies, weight gain, hypoglycemia, edema, anemia, and congestive heart failure [11; 12]. Therefore, it is necessary to look for alternative medications with fewer or no side effects. Complementary and alternative medicine approaches that include herbs may prove to be promising. Several medicinal herbs have been used in traditional medicine for many years to improve or prevent diabetes. Bitter melon, aloe vera [9], ginseng [10], fenugreek [12], and fig leaf [11] are some of the commonly used herbs to manage diabetes. Several studies have shown that _Olea europaea_ leaf extract is involved in multiple biological activities, such as the reduction of free radicals during tissue injury, normalization of the lipid profile, increase in immune function, lowering of the blood glucose level and blood pressure, decrease in arrhythmia, and prevention of intestinal muscle spasms, antioxidant and antimicrobial effects [13; 14; 15; 16].