Smoking-related metallic taste: The patient's history of smoking is a strong indicator for this diagnosis, as smoking is a common cause of metallic taste due to its effect on the taste buds and oral mucosa.

Medication side effect: Certain medications, such as antibiotics, antihistamines, and decongestants, can cause a metallic taste in the mouth. Although not specified, the patient might be taking such medications.
Gastroesophageal reflux disease (GERD): Stomach acid flowing up into the mouth can cause a metallic taste. This condition is common and could be related to the patient's smoking history.
Nutritional deficiencies: Deficiencies in vitamins like zinc or vitamin B12 can lead to changes in taste, including a metallic taste.

Lead or heavy metal poisoning: Although less common, exposure to lead or other heavy metals can cause a metallic taste. Given the patient's occupation ("bet ca work up"), there might be an occupational exposure risk.
Neurological disorders: Certain neurological conditions, such as multiple sclerosis or Parkinson's disease, can affect the sense of taste. While less likely, these conditions are critical to diagnose early.
Cancer: Head and neck cancers, or cancers affecting the oral cavity, can cause changes in taste. Given the patient's smoking history, which is a risk factor for many types of cancer, this is a diagnosis that must not be missed.

Sjögren's syndrome: An autoimmune disorder that can cause dry mouth and alterations in taste, including a metallic taste.
Hypothyroidism: Some patients with hypothyroidism report changes in taste, which can include a metallic taste.
Wilson's disease: A rare genetic disorder that leads to copper accumulation in the body, potentially causing a metallic taste among other symptoms.