Lindsay Lohan beaming at a previous court appearance.

The 26-year-old actress has reportedly insisted she will only enter a court ordered treatment facility if she is allowed to have the prescription drug - used to treat Attention-deficit/hyperactivity disorder - which she claims she needs to function, according to TMZ.

The troubled starlet was recently sentenced to 90 days in rehab after pleading "no contest" to charges for lying to police about driving during a car crash last June but has jetted to Brazil for some partying and promotional appearances before entering the facility, which has horrified her father.

Michael Lohan has posted an open letter to the actress's booking agent Mike Heller, whose father is her lawyer Mark Heller, warning him that he will be held fully responsible if anything happens to Lindsay, who was reportedly spotted "out of it" in a Sao Paulo nightclub with her dress up around her waist and crying underneath a table.

He wrote: "I am telling you now if you are with Lindsay in Rio or you booked it, and anything happens to my daughter, I am holding you personally responsible. Judging from what has happened to in the past, and the way she looks down there from the pictures in the media, it's not a good thing.
If you have anything to do with her being there, its on you. Count on it. (sic)"