These leaves are both bitter and astringent, but extremely good for your health.

According to Traditional Medicine Practitioner Bui Dac Sang of the Hanoi Traditional Medicine Association, guava leaves are considered a "miracle cure" because they contain many beneficial compounds. Young guava leaves or young shoots contain about 3% resin and 7-10% tannin, antioxidants such as vitamin C and flavonoids, and antibacterial and anti-inflammatory substances.

Guava leaves help lower blood sugar levels by preventing the body from absorbing sucrose and maltose. Studies have also shown that guava leaves can improve symptoms of diabetes such as hyperinsulinemia and insulin resistance. You can use guava leaves by brewing them into a tea and drinking it daily for 12 weeks to see noticeable results.

Guava leaves are also used in the treatment of allergies. Compounds in guava leaves inhibit the release of histamine – the main cause of allergies. Guava leaves stimulate the production of digestive enzymes, help kill bacteria in the intestinal lining, and prevent the growth of toxic enzymes produced by bacteria.

In Traditional Chinese Medicine, guava leaves are a herbal remedy for diarrhea. To treat diarrhea, boil 30g of guava leaves with a handful of rice flour in 1-2 cups of water and drink twice a day. For dysentery, cut the roots and leaves of a guava tree, boil for about 20 minutes, filter the liquid, and drink daily until symptoms subside. To relieve stomach pain, boil 8 guava leaves in 1.5 liters of water and drink three times a day.

Guava leaves are effective in removing pimples and dark spots on the skin. Guava leaves contain antiseptic properties that kill acne-causing bacteria. To use, wash the leaves thoroughly, crush or grind them into a paste, and apply it to pimples after cleaning the skin. For blackheads, crush guava leaves, mix with warm water, and wash the affected areas daily, gently rubbing to remove them quickly.

Due to its anti-inflammatory properties, guava leaves are often used as an ingredient in toothpaste, to cool the mouth, relieve toothache, treat gum disease, mouth ulcers, and sore throats. You can also rinse your mouth with guava leaf tea or make a natural guava leaf paste at home to brush your teeth.

Scientists at Krupanidhi Medical University in India have discovered that a powder extract from guava leaves can protect the liver from damage. Tests on mice showed that those fed the guava leaf extract avoided liver damage caused by chemicals, while those not fed the extract suffered severe liver damage. Experts believe that the antioxidants in guava leaves are responsible for this preventative effect.

People use guava leaves to make tea, which is exported to European and North American countries. To prepare a cup of guava leaf tea, steep a handful of guava leaves in hot water for about 15 minutes, strain the water, and discard the leaves. Boil this water with tea leaves to drink, or steep green tea leaves in hot water and drink the resulting infusion throughout the day for health benefits.