Michael Douglas' son must stay in jail until at least 2018, a court has ruled.

Cameron Douglas had appealed against a 2011 decision to extend his five-year sentence - which was issued in 2010 for heroin possession and conspiracy to distribute narcotics - by an additional four-and-a-half years because of drug infractions whilst behind bars, but a hearing yesterday (15.04.13) ruled that Judge Berman was justified in giving him an ''unusually long sentence''.

The three-judge appeal panel went on to say 34-year-old Cameron is ''an example of a defendant who has shown himself to be a poor candidate for treatment or leniency.''

The 34-year-old actor - whose mother is Michael's ex-wife Diandra Morrell Douglas - was given the original five-year sentence after co-operating with authorities, reducing the term from the expected 10 years.

However, in 2011, he received the extra jail time after being caught with drugs in prison then lying about how he ended up in possession of the narcotics.

Appealing the sentence last December, Cameron's attorney, Paul Shechtman, described the punishment as ''shockingly long'' and ''maybe the harshest sentence ever imposed on a federal prisoner for a drug possession offence.''