**7. Conclusion**

For centuries, medicinal plants have been used worldwide for the treatment of several diseases. In South American populations, plant products significantly contribute to primary health care and are sometimes the only therapeutic resources of some communities and ethnic groups.

Among the medicinal species used in South America populations, *M. glomerata* and *M. laevigata* are especially important due to their relevant therapeutic properties. In popular medicine, both species have a long history of use, and they are still employed especially for the treatment of respiratory diseases.

Pre-clinical trials have been conducted on guaco extract that have revealed scientific evidence for its anti-inflammatory, anti-allergy, and bronchodilation properties. However, there are currently no clinical studies for assessing the efficacy of guaco extracts and preparations in patients who present respiratory complaints.

Both guaco species have many bioactive compounds that probably contribute to the pharmacological effects. Thus, the properties of guaco should not be attributed only to coumarin because high contents of kaurene diterpenes and cinnamic acid derivatives were found in the extracts. Studies involving the quality control of different brands of guaco phytomedicines and extracts have been conducted and have shown a wide variation in the content of the main metabolites. A number of studies have reported that this discrepancy is due to the geographic origins, agronomic aspects, extractor solvent and extraction techniques of the guaco. Therefore, depending of the region and period of plant collection, the effects and/or toxicity of guaco may change or not be evident.

Regarding the safety of the extracts, phytomedicines and isolated compounds, guaco species did not present significant toxic and genotoxic effects in humans. However, the majority of studies were conducted in rat and mice, which have a unique metabolism, suggesting that new studies must be conducted. Additionally, relevant information on metabolism, bioavailability and toxicity has only been reported for coumarin, without substantial information concerning the other main metabolites.

In general, is possible to conclude that there is a need for clinical studies using standardized phytomedicines or extracts. This may be the most important step to ensure conclusive studies of guaco species. By conducting clinical studies, it will be possible to know the most effective extract for therapeutic purposes and to correlate the metabolite content with its relevance in a pharmacological and toxicological context. Meeting this requirement will guarantee the benefits and safe use of guaco.
