Michael Lohan is convinced the Mean Girls star has become dependent on medication and he's compiled a list of physicians he claims are responsible - and he wants California's Attorney General Jerry Brown to question them.

In a letter sent to Brown, obtained by TMZ.com, Lohan and his lawyer Lisa Bloom "respectfully request an investigation" into the "unscrupulous doctors" who "overprescribe medications to (Lohan)... in violation of California law".

Lohan also claims his daughter has found a "giant legal loophole" to obtain her medications.

A recently leaked probation report revealed the actress regularly medicates anxiety and depression with a cocktail of painkillers and has been on the same prescriptions "for as long as she can remember".

She is currently serving time behind bars after violating probation stemming from a 2007 DUI arrest. She has been ordered to attend a rehab programme upon her release.