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Herb library · Herb · Mikania glomerata

Guaco

A climbing vine of Brazil whose leaves are made into cough syrups and teas that are widely sold there. It has been tested for safety in healthy volunteers, but no trial has tested whether it helps a cough.

Traditional use

Reviewers of its research record that Indigenous peoples of Brazil have an ancient tradition of using guaco for snakebite, and that in Brazilian herbal medicine today the leaves are used for coughs, colds, bronchitis and asthma, mostly as a syrup or tea. The two species sold as guaco, Mikania glomerata and Mikania laevigata, are used interchangeably.

What studies show

  • Insufficient

    Coughs, bronchitis and asthma: no trial in people has tested whether guaco helps. Its extracts relax airway muscle and reduce inflammation in animal and lab studies.

  • Limited

    Safety: in a 2023 trial in 19 healthy volunteers, two weeks of oral solutions of each species at two doses caused no serious side effects; one person had heartburn, and blood tests stayed in the normal range, though Mikania laevigata shifted several measures, including clotting times.

Be careful of

Cautions

  • InteractionGuaco leaves are rich in coumarin, and a lab study found Mikania laevigata extract slowed blood clotting. If you take warfarin or another blood thinner, do not use guaco without your clinician.
  • NoteIn Mexico and Central America "guaco" can also mean vines of the genus Aristolochia, which contain aristolochic acid; the FDA blocks such products at the border because they have caused outbreaks of kidney failure. Make sure a product names Mikania.
  • PregnancyNo safety information for pregnancy or breastfeeding was found; avoid it then.
  • Ask a clinicianTalk with a clinician or pharmacist before using this if you take prescription medicines, are pregnant or breastfeeding, or are giving it to a child. A cough that lasts more than three weeks, or comes with fever or trouble breathing, needs a clinician.

Sources

  1. Safety evaluation of Mikania glomerata and Mikania laevigata in healthy volunteers: a randomized, open label and multiple dose phase I clinical trial (J Ethnopharmacol, 2024) — PubMed record (opens in a new tab) · NIH · read September 25, 2026
  2. A kinetic study of the main guaco metabolites using syrup formulation and the identification of an alternative route of coumarin metabolism in humans (PLoS One, 2015) — PubMed record (opens in a new tab) · NIH · read September 25, 2026
  3. In Vitro Anticoagulant Activity of Mikania laevigata: Deepening the Study of the Possible Interaction Between Guaco and Anticoagulants (J Cardiovasc Pharmacol, 2019) — PubMed record (opens in a new tab) · NIH · read September 25, 2026
  4. Trypanocidal constituents in plants 1. Evaluation of some Mexican plants for their trypanocidal activity and active constituents in Guaco, roots of Aristolochia taliscana (Biol Pharm Bull, 2002) — PubMed record (opens in a new tab) · NIH · read September 25, 2026
  5. Import Alert 54-10 (products that contain aristolochic acid) (opens in a new tab) · FDA · read September 25, 2026
  6. Scientific evidence for Mikania laevigata and Mikania glomerata as a pharmacological tool (J Pharm Pharmacol, 2010) — PubMed record (opens in a new tab) · NIH · read September 25, 2026

Reviewed September 25, 2026.