Just because everything looks like Mario Kart, doesn't mean it is Mario Kart. You may feel utterly in control driving after a few spliffs or a pill, but you're not. And the police can usually spot the signs of someone high and HGVing.

How do drugs affect driving?

Well, let's face it. None of them make you better drivers - however Lewis Hamilton-y you feel at the time.

Cannabis slows your reaction times and screws up your judgement of time and distance. And you'll find it hard to keep up the levels of concentration needed to drive safely.

Cocaine makes you more prone to speed and do aggressive manoeuvres because you'll be feeling more confident. When you're on a coke comedown, you're likely to be drowsy and easily distracted.

Ecstasy will distort your vision and heighten sounds. Your risk judgement abilities will be cruddy, and you'll be more aggressive in your driving style.

Mixing any drugs with alcohol will make your driving abilities even more unpredictable.

How do police judge if you're driving on drugs?

Police are pretty good at spotting drivers under the influence and can stop and observe you for outward signs of impairment caused by drugs or alcohol.

The first thing they usually check are your eyeballs. The size of your pupils can usually give you away. If you're on opiates, your pupils can get all small like pinpricks. If you're on stimulants, your pupils are likely to be huge.

Your co-ordination skills will be tested too. For example, you may be asked to close your eyes and touch your nose, or stand on alternate feet whilst counting aloud to 30.

Refusal to participate in the tests is an offence in the same way as failure to provide a breath test under suspicion of drink driving.

If you're taken to a police station

If you fail the road-side field impairment tests, you could be arrested and taken to the police station. Here, you may be tested for the presence of drugs through a urine or blood sample, with your written consent. A doctor can also carry out a test to see if you've been incapacitated due to medical reasons, such as illness or intake of prescribed medicine.

What's the punishment for drug driving?

Penalties are pretty severe. You're facing a minimum 12-month driving ban, a £5,000 fine and potential prison time.

These penalties can have a butterfly effect on the rest of your life. Your car insurance will rocket, you'll have to tell any future employer you have a criminal conviction, and countries like the USA won't let you in.

If you accidently kill someone through driving dangerously, you're looking at a 14 year prison sentence.

Is it illegal to drive whilst taking medicine?

Even if the drug is legal, driving on it is just as illegal as driving on prohibited drugs. If a medicine affects your ability to drive, you'll be breaking the law if you get behind the wheel.

Always read the label if you're taking prescribed medication. Antihistamines (often used in flu and hayfever remedies) and tranquillisers (used to treat anxiety, depression and sleeping disorders) may significantly affect reaction times and/or cause drowsiness. If the label advises against 'operating heavy machinery', consider it a warning not to get behind the wheel of a vehicle. If in doubt, consult your doctor (GP).

Updated: 22/10/2012