The law of drug driving changed recently and is complex. You can be guilty of drug driving if you have a certain amount of an illegal drug in your system. Equally, if you have too large an amount of a legal or prescription medication in your system, you may also be guilty of an offence. This is a strict liability offence and does not require any proof that you were UNFIT through the drugs in your system. The old law of driving whilst unfit through drugs is still in existence and will often require expert evidence to assist in defending your case.