Ollie's advice is brilliant - while Roaccutane (otherwise known as Accutane/Isotretinoin) can cause dry lips/achy joints/mood swings its most potent side effect is on the liver. It is a Retinoid, Vitamin A derived which means you are increasing your Vitamin A intake to very very high levels. If you've ever read in SAS Survival Guides, it says never eat the liver of a polar bear (yes, it really does :P) because it contains dangerous levels of Vitamin A and will kill you. Accutane contains much lower levels, but it is still a very very high dose and so it is absolutely IMPERATIVE that you have regular blood tests and liver checks.
For this reason DO NOT buy Accutane over the Internet, the after care service could save your life if your liver becomes intolerant to it.
However, as many have stated, Accutane is very effective in clearing up cystic acne, but personally I would advise you only to go on it for severe acne as the benefits have to outweight the potential side effects. If you have mild to moderate acne, a less aggressive regimen of Benzoyl Peroxide may be more appropriate.
But on Accutane: it MUST be taken under dermatologist supervision!