Background: S. alopecuroides, Z. officinale and M. officinalis are used traditionally in the treatment of pain. Objective: To evaluate the plants effects in the rat formalin test and their activity on the opioid receptors. Methods: Each rat was placed individually in a cage for 30 min to get acclimated. Then 0.05 mL of 10% formalin was injected subcutaneously into the dorsal surface of the right hind paw of the rat. Afterward, the animal was returned to the cage for observation. Pain responses were scored at 30 and 60 min after formalin injection. 90% ethanol extract was injected subcutaneously 30 min before formalin injection. To evaluate the role of opioid receptors in the analgesic effect of the extracts inhibiting the early phase of the test, naloxone was injected subcutaneously 30 min before extract injection. Moreover, the extracts effects on the Straub reaction were studied in mice. Mice were placed in individual cages immediately after extract injection for observation. The positive Straub tail response was considered as a persistent elevation of the tail at an angle more than 45º, 30 min after extract injection. Results: S. alopecuroides and M. officinalis inhibited both phases of the formalin test (p<0.05), but Z. officinale inhibited only the late phase (p<0.05). Naloxone did not reverse the effects of S. alopecuroides and M. officinalis in the formalin test. Further, the extracts did not cause Straub reaction. Conclusion: The plants have analgesic effect without opioid including µ2 receptor activity and may not produce the side effects caused by activation of µ2 receptors.

 
The use of herbal medicines dates back to the beginning of the human history. Today, herbal medicines still play a significant role in the prevention and treatment of disease in many cultures and communities. There are few reports about adverse effects of herbal medicines. This is why many people around the world believe that herbal medicines can't cause adverse effects. They believe plants are safe, even if they're not efficient. This idea is wrong, regardless of how common it might be considered. Plants can be dangerous and even lethal in some cases. It is not just plant chemicals that might cause adverse effects. The role of environmental pollutants and the presence of fraud in form of alternation and adulteration in herbal preparations is another factor that might contribute to harmful effects on various organs of the body, including the kidneys. Kidneys are vital organs that filter blood, remove wastes and excrete the wastes in the urine. They are susceptible to injury because of their high exposure to different chemical substances including chemicals from the herbs. This is why studying the possible adverse effects of herbal medicines on kidney structure and function gets important. This issue highlights the role of regulatory and legislator organizations in providing up-to-date laws to help maintain a better regulation on the production and consumption of herbal products. This article reviews the findings on this case. We used papers published between 1990 and January 2018 in pubmed and google scholar databases.