Sometimes, the consumption of local made alcoholic beverages may cause blindness or even death. This may be because of contamination of the beverages with :

The consumption of illicit or locally made alcoholic beverages can lead to blindness or death due to contamination with methyl alcohol (methanol). Methanol is often added to industrial ethanol to make it 'denatured' and unfit for drinking [1]. In the body, methanol is metabolized by alcohol dehydrogenase into formaldehyde and subsequently into formic acid [t2, t6]. Formic acid is the primary toxicant responsible for metabolic acidosis and ocular toxicity [t1, t4]. It specifically targets the optic nerve and retinal ganglion cells, leading to permanent blindness [c1, t3]. Because the liver prioritizes the metabolism of ethanol over methanol, ethanol is sometimes used as a treatment to block the production of these toxic metabolites [t1, t6]. Even small quantities, such as 10 mL of methanol, can be lethal to adults [t8].

Sources

1. [1] Science , class X (NCERT 2025 ed.) > Chapter 4: Carbon and its Compounds > How do alcohols affect living beings? > p. 72