It's Friday night, the pub's just closed and you're back at someone's flat, five pints deep with a blue bag of tins in your hand. "Is anyone gonna put the call in?" grins one of your friends.

Everyone chucks £20 on the table, you make the call, and an hour after you were told you'd have it, you pop outside to meet two sullen men in a blacked-out X5, who take your cash and hand you a few wraps of cocaine. This may well happen again at 4AM, and possibly even again at 7AM. Either way, you're not getting up before two the following afternoon, and when you do it'll feel like someone's taken a microplane to the inside of your nose.

You are not alone. Apparently, this is what we do. A lot. London has just been declared the "Cocaine Capital of Europe" for the second year running. Researchers from the EU's drugs monitoring agency tested our sewage and found an average of 909mg of cocaine per 1,000 people daily in London – up from 737mg in 2014, and well ahead of Amsterdam, the next most gak-heavy city, which had 642mg.

So what's all this cocaine consumption doing to our bodies? We tend to hear a lot of lurid stories about what happens when you plough through four grams a day – you get coke-bloat; your septum disintegrates; your heart explodes – but that's not how most people actually use the drug. What about the casual user? What about the person doing a gram or half a gram every weekend or fortnight over a period of years? What about you?

Dr Adam Winstock, a Consultant Psychiatrist and founder of the Global Drugs Survey, is clear: "Doing a gram of coke every weekend is not healthy, nor can it even really be called casual or average use," he says. "That's something we call normative misperception, where someone thinks, 'My mates and I are behaving like this, therefore everyone else must be as well – it's totally normal.' Cocaine is a vasoconstrictor – it makes the heart pump faster while narrowing the blood vessels. It's like putting your foot on the accelerator while pinching the fuel line. People also forget that sharing a rolled up note that everyone is sticking into bloody nostrils can transmit Hepatitis C, which is a hardy little virus that lives outside the body for weeks."

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Dr Henry Fisher, a chemist who is now Head of Policy at VolteFace, elaborates: "Doing cocaine every weekend is more dangerous than a chemical like MDMA. Cocaine works your heart really hard, inflicting tiny, micro-lacerations on your heart muscles, essentially due to over-exercise. Over time these get worse and worse, turning into scar tissue as you age... then there's the whole issue of atherosclerosis."

Atherosclerosis, it turns out, is where your arterial walls begin to thicken until they begin to resemble fatty, well-marbled steaks. Not quite the height of Miami Beach glamour.

Dr Winstock is keen to point out that there are many complicating factors. "Obviously, if you're an overweight, 50-year-old smoker, your heart will be under more pressure than if you're a 20-year-old athlete. But even so, the danger here is about prolonged use over years. It's also about how you use the drug," he says. "Findings from the Global Drugs Survey, collating evidence from over 50,000 drug users over several years, suggest that, on average, 0.5 percent of cocaine users find themselves in hospital with acute reactions to the drug – and users in most countries get, on average, about ten lines out of a gram. But in Brazil they average six lines per gram, and their rate of acute hospital admissions is 3.5 percent. So it's fairly obvious that doing smaller, more frequent bumps is easier on the heart than railing massive fat lines."

Both Dr Winstock and Dr Fisher agree that many of the hazards of prolonged cocaine use are to do with mental and emotional wellbeing as well as physical harm. "As people use more and more, over longer and longer periods," Dr Winstock explains, "relationships can start to fall apart. The user's bank account drains, performance at work goes downhill, romantic partners get angry and friends begin to distance themselves – so they feel lonely and isolated, often leading them to do even more coke to get that false ego boost."

Dr Fisher puts it even more succinctly: "One of the major effects of cocaine is to make people act like dickheads." He then underlines the seriousness of the point: "People don't realise what a slippery slope it is. Users become reliant on that fake confidence that cocaine can give. So it starts with people doing it every weekend, then gradually they begin to need that bump on a Thursday instead of a Friday. Then it becomes Wednesday, and so on, until you have a really serious problem."

Neil Woods, a former detective who spent 14 years undercover busting drug dealers, now campaigns for LEAP UK, an organisation of current or former police opposed to prohibition. He adds a different perspective: "Many of the dangers of using cocaine come from what it's mixed with. First of all, people very often use coke when they're drinking, allowing them to consume far more alcohol than usual. Not only does this increase the risk of volatile and aggressive behaviour, but cocaine and alcohol combine in the liver to form a new chemical, cocaethylene, which heightens and prolongs the effect of both drugs."

And the problem worsens: it's not just about cocaine; it's about all the other stuff added to the the wraps we buy.

"There are as many as 16 chemicals added to cocaine. Purity varies wildly, with a very rough average for a gram in the UK at around 10 percent," Woods continues. "The chemical levamisole is usually added at source, early in the production process. This was developed as a de-worming agent for cattle, and is really not good for white blood cells in humans. Then the dental anaesthetic, lidocaine, is often used as a bulking agent, which is widely believed to be carcinogenic if used regularly. Obviously these aspects would be much safer if cocaine were available as part of a properly regulated market. Interestingly, the only recent year in which deaths from cocaine fell was 2008-9, when mephedrone was available as a legal high. As soon as the government banned that, coke deaths began climbing again."

There you go: the familiar story of the government worsening drug harms by enforcing prohibition.

So I hope that makes you feel better, now you know what's actually happening to your body every time you get a gram in. Hope the thought of your arteries shrivelling and stiffening as you shovel cattle de-worming agent into your nostrils isn't too much of a bum out. Have a great Friday night!