A bitter taste in the mouth primarily stems from:

• Acid reflux (GERD): An acid reflux will cause acidic tastes to come back into the mouth. The bitter or sour taste can linger in the mouth for some time. This condition is often associated with heartburn, which occurs due to the relaxation of the lower oesophagal sphincter.
• Dehydration: Not drinking enough water dehydrates the mouth and produces concentrated secretions in the body that alter the sense of taste. With water deficiency and less salivary secretion, the mouth cannot clean itself naturally, and bacteria flourish.
• Infections: Respiratory tract infections, such as sinusitis or the common cold, may result in postnasal drip. These can give rise to a foul or bitter taste in the mouth as a secondary effect. Bacterial or fungal infections affecting the mouth, throat, or gums can also alter taste perception.
• Side Effects of Medication: Drugs like antibiotics and gilt are reported to impart a persistent bitter taste because there are compounds that attach to the taste receptor. Changes in the composition of saliva are also responsible for a bitter taste and dryness of the mouth in some cases.
• Poor Oral Hygiene: Plaque accumulation, gum disease, and untreated cavities may all cause bacteria to flourish in the mouth and produce a metallic or bitter taste. Regular brushing, flossing, and seeing the dentist prevent these conditions.
• Clogged Liver: If the liver has failed to detoxify the body reasonably well, toxins accumulate and then can generate a bitter taste. According to Ayurveda, this is due to aggravated Pitta dosha, generally considered to be associated with excessive heat and poor digestion.
• Poor Digestion and Ama Accumulation: Poor digestion leads to the development of Ama, which can give rise to a bitter taste in the mouth. When the Agni (digestive fire) is weak, undigested food ferments in the gut and induces the accumulation of metabolic wastes.
• Bile Reflux: It is another condition in which the bile from the liver flows back into the stomach and from there into the oesophagus, causing a bitter or burning sensation in the mouth and throat. Its aetiology is often connected with problems arising from the gallbladder or dysfunctions in the gastrointestinal tract.
• Overeating Spices, Fried Foods, Fermented Items, or Sour Foods: Eating too much spicy, fried, or sour increases the Pitta and bile in the system, resulting in bitterness in the mouth. Fermented foods certainly help in small amounts, but larger amounts can throw off the balance in our guts.
• Dental Issues: Dental problems like gingivitis, periodontitis, and abscesses can elicit a bad or metallic taste as a side effect of the activity of the bacteria. Neglecting oral hygiene can breed bacteria, contributing to halitosis and altered taste perception.
• Smoking and Drinking Alcohol: Smoking and drinking both suppress saliva production and impair taste bud functioning. Slight bitterness may linger in the mouth even after the drug is gone. Smoking increases the risk of developing gum disease and oral infections, further complicating matters.