If you’re the type of person who usually doesn’t smoke but then can’t resist lighting up once you’ve had a drink, then you’ve got your brain to thank for that.

It’s a tale as old as time, you quit smoking years ago, you hardly even think about it anymore and then – boom – four pints you’re hit with a craving so strong it stops you in your tracks.

But why does it happen? Well, there’s a couple of things going on. Firstly, your previous nicotine intake has affected your memory. And secondly, your dopamine levels have dropped.

According to a 2009 study by Dr John Dani and researchers from University of Pennsylvania, nicotine has a stronger impact when forming neuronal connections.

Dr Dani explained: “Compared to injections of saline, nicotine strengthened neuronal connections, sometimes up to 200 percent.

“And this strengthening of connections underlies new memory formation.”

So, for all those years you did smoke and drink you were inadvertently setting up fond memories. And now when you start drinking again, that bit of your memory reminds you of this and you start to crave nicotine – much to the annoyance of your pals who smoke who end up handing out cigs to you without you ever returning the favour.

Secondly, both alcohol and nicotine boost dopamine in the brain, which makes you feel happier.

At this point, you may be thinking ‘well if I have cigarettes and booze together I’ll be even happier, right?’

Wrong – at least according to another study by Dr Dani, which looked at the dopamine levels in rats and found the rats who were given nicotine consumed more alcohol but didn’t see a spike in their dopamine levels.

In short – the study found that mixing alcohol and nicotine actually made you less happy.

Not only that, Dr Dani noted that people can then end up drinking and smoking more because they’re keen to up their dopamine levels, resulting in a bit of vicious cycle.

Of course, the best thing to do for you health is to avoid smoking altogether and Dr Dani urged so-called social smokers to knock it on the head.

He told Vice: “What you’re describing is called a ‘chipper’—somebody who doesn’t smoke very often but will under certain circumstances.

“And what I’d recommend is that you just don’t. Because it’s really, really common for that habit to slide into regular use. And then it’ll be really hard to give up.”