Betel nut can be chewed alone, but it is often chewed in combination with other ingredients (called a "quid") including calcium hydroxide, water, catechu gum, cardamom, cloves, anise seeds, cinnamon, tobacco, nutmeg, and gold or silver metal. These ingredients may be wrapped in a betel leaf, followed by sucking the combination in the side of the mouth. It is reported that ingestion of 8-30 grams of areca nut may be deadly.
Betel is not recommended in children due to risks of toxicity, including worsening symptoms of asthma, effects on the heart, and cancer.
Breathing problems with betel nut use have been reported, although no allergic reactions are noted in the available scientific literature. Caution is warranted in people with allergies to other members of the Palmaceae family.
Betel nut cannot be considered safe for human use by mouth. This is due to toxic effects associated with short or long-term chewing or eating of betel nut.
Betel nut and chemicals in betel leaves may cause skin color changes, dilated pupils, blurred vision, wheezing/difficulty breathing, and increased breathing rate. Tremors, slow movements, and stiffness have been reported in people also taking anti-psychotic medications. Worsening of spasmodic movements has occurred in patients with Huntington's disease. Seizure has been reported with high doses.
"Cholinergic" toxicity symptoms from betel use may include salivation, increased tearing, lack of urinary control (incontinence), sweating, diarrhea, and fever. Other problems may include confusion, problems with eye movement, psychosis, amnesia, stimulant effects, and a feeling of euphoria. Long-term users may form a dependence on the effects of betel, and discontinuing use may cause signs of withdrawal, such as anxiety or memory lapse.
Chewing betel nuts can also cause nausea, vomiting, diarrhea, stomach cramps, chest pain, high or low blood pressure, and irregular heart beats. A heart attack occurred in a man immediately after chewing betel nut. It is not clear if betel was the cause.
Betel chewing has been shown to have a harmful effect on the gums. The nut may cause the teeth, mouth, lips, and stool to become red stained. Burning and dryness of mouth may occur.
Studies of Asian populations have linked pre-cancer conditions of the mouth and esophagus to betel use ("oral submucous fibrosis"). There may be a higher risk of cancers of the liver, mouth, stomach, prostate, cervix, and lung with regular betel use.
In animals, a chemical in betel nut alters blood sugar levels. Although human study is lacking in this area, caution is advised in people with diabetes or glucose intolerance, and in those taking drugs, herbs, or supplements that affect blood sugar. Serum glucose levels may need to be monitored by a healthcare provider, and medication adjustments may be necessary. Betel nut chewers may have a higher risk of developing type 2 diabetes. Animal studies show mixed effects on thyroid function and increased skin temperature. Other problems can include increased blood calcium levels and kidney disease ("milk alkali syndrome"), possibly due to calcium carbonate paste sometimes used for preparing betel nuts for chewing.