Lindsay Lohan's disastrous Saturday Night Live performance was due to prescription drugs, her father has claimed.

Michael Lohan claims the troubled actress is no longer taking any illegal substances but says medicine provided by her doctors prevented her from showing her true acting ability when she performed on the comedy sketch show in March.

However, Michael insists he convinced her to stop taking prescription medication ahead of her recent Glee cameo and believes she is now once again showing her potential.

He told Celebrityviplounge.com: ''I have to say this...on SNL, Lindsay was not using any illicit drugs or drinking but she still is on prescription drugs that they gave her. And the meds that they give her are meds that they say she needs, but she doesn't need them. But they kind of make her flat. She's not acting at a full potential. It's like the screen is down over her.

''And now when she did Glee, I said, 'Linds, get off the damn medication and let people see who you really are.' And for a couple days before Glee, she went off this stuff. And there were tears in my eyes when I watched Glee. THAT was Lindsay. Yeah that was her acting. That is Lindsay Lohan at the Parent Trap, Freaky Friday, and Mean Girls potential. That is what she was.''

In 2010, Lindsay's probation papers indicated she was on antidepressants Zoloft and trazodone, stimulant Adderall, Nexium for acid reflux, and painkiller Dilaudid for dental problems.