MS-2920

A 29-year-old man newly diagnosed with epilepsy visits his GP with complaints of fatigue. He has no significant medical history except for taking oral phenytoin and loratadine seasonally. He works as a construction site worker and has been experiencing a lot of stress at work due to the need to work extra shifts. During the consultation, he appears anxious and has a slim build. His blood test reveals macrocytic anaemia.

What could be the probable reason for his symptoms and blood results?