Vitamin B12 Deficiency: This condition is known to cause macrocytosis (large red blood cells) due to impaired DNA synthesis. Neurological manifestations, including visual hallucinations, can occur due to the deficiency's impact on the nervous system.

Alcohol Use Disorder: Chronic alcohol abuse can lead to macrocytosis. Visual hallucinations can be a part of alcohol withdrawal syndrome or a manifestation of Wernicke's encephalopathy, a condition associated with thiamine deficiency often seen in alcoholics.
Hypothyroidism: Although less common, severe hypothyroidism can cause macrocytic anemia. Visual hallucinations are not typical but can occur in the context of myxedema madness, a rare complication of untreated hypothyroidism.

Cobalamin Deficiency due to Gastric Bypass or Malabsorption: Similar to vitamin B12 deficiency, but with a specific cause that needs timely intervention to prevent long-term neurological damage.
Pernicious Anemia: An autoimmune cause of vitamin B12 deficiency that requires specific treatment to prevent progression of neurological and hematological symptoms.

Nitrous Oxide Abuse: Can cause vitamin B12 deficiency and subsequent macrocytosis, along with neurological symptoms including hallucinations.
Methotrexate Toxicity: This chemotherapeutic agent can cause macrocytosis. While less common, neurological side effects including hallucinations can occur, especially at high doses or with prolonged use.
Leukemia or Myelodysplastic Syndromes: Certain types of these conditions can present with macrocytosis. Hallucinations could be a symptom of advanced disease or treatment side effects, though this is less direct.