We need a fair policy for dealing with drivers whose ability is impaired by drugs, such as cannabis, amphetamines and cocaine. Setting limits for driving under the influence of drugs may be difficult. Tests would be necessary for the levels in the blood of each of these drugs. But, such limits may not reflect the complex interactions between drugs and their effect on driving: a driver may be severely impaired but under the limit for each individual drug. Also, setting a legal limit for the use of a substance that is illegal seems self-contradictory. So to solve the problem of drug-driving there should be a new offence of driving with any level of illegal drug in the body. This would make it much easier to catch and convict drug-drivers – the ultimate deterrent.