Photo: TMZ

FROM TMZ: Lindsay Lohan's drinking problem has returned with a vengeance -- sources close to the actress tell TMZ, she's been boozing heavily for months now ... as much as TWO LITERS of vodka a day. 

According to sources,  Lindsay's become so stressed by her dire financial situation and the impending probation violation -- stemming from her PCH crash this summer -- that she's turned to alcohol for relief.

We're told Lindsay -- who's struggled with substance abuse in the past and even has a DUI conviction under her belt -- would often begin drinking first thing in the morning, and continue drinking throughout the day.

Read more at TMZ