Lifestyle and exercise

Alcohol intake 'linked to risky sex'

“Alcohol is to blame for unsafe sex,” the Daily Mirror has announced. The newspaper reported that “Sexual desire is boosted by booze and researchers believe thrill-seekers are naturally drawn to drink and unprotected sex.”

The story, which highlights an important issue during the Christmas party season, is based on a review of studies that looked at whether there was an association between blood alcohol content and the likelihood of using a condom during sex. By pooling the results from 12 studies the researchers found that every increase in blood alcohol of 0.1mg/ml resulted in an increase of around 3% in the likelihood of having unprotected sex.

In the studies, participants were grouped at random to receive different amounts of alcohol or a placebo (a non-alcoholic substitute). They were then asked about their intentions to engage in unprotected sex. The nature of such studies means they may not reflect real-life situations. Nevertheless, the health message remains the same.

A spokesperson from the Terrence Higgins Trust was quoted in the Mirror as saying: “We all know that drinking to excess can make you do stupid things.” Their advice is: “If you can’t stay sober, stay safe – carry condoms and use them.” Condoms can protect against unplanned pregnancy and are the most effective protection against sexually transmitted infections.

Where did the story come from?

The study was carried out by researchers from the University of Toronto and was funded by the US National Institute for Alcohol Abuse and Alcoholism. It was published in the peer-reviewed medical journal Addiction.

The Daily Mirror covered this study, but did not report any data from the study. It’s not clear from the research whether alcohol boosts sexual desire, as the Mirror suggests, because it focused on loss of inhibition and the likelihood of intending to have unprotected sex.

What kind of research was this?

This systematic review and meta-analysis pooled the results from many randomised controlled trials to assess to what extent the likelihood of having unprotected sex was influenced by drinking alcohol. The researchers said they were interested in this because alcohol use is associated with the risk of getting HIV and other sexually transmitted infections. One theory is that alcohol reduces inhibitions, which leads to risk-taking behaviour. However, the researchers say that this kind of research is difficult because people who drink more alcohol and have unsafe sex may have higher-risk personality traits than others. This means that they may have characteristics that put them at higher risk of both activities, rather than alcohol causing them to have risky unprotected sex when they normally wouldn't do so.

The researchers wanted to see whether alcohol had an independent effect on subsequent sexual behaviour (the intention to use a condom). They also wanted to see whether the risk of unsafe behaviour would increase if the amount of alcohol in the bloodstream increased.

What did the research involve?

The researchers searched various medical and scientific databases for keywords relating to alcohol, sex and sexually transmitted infections. Additionally, they looked at keywords relating to the participants’ willingness to use condoms or to make decisions about safe sex. They searched for studies published up to May 2011. Eligible studies had to meet all of the following criteria:

  • The study had to be published in a peer-reviewed journal.
  • Studies had to be randomised controlled trials, where people were randomly assigned to receive placebo or alcohol.
  • Studies had to have experimentally manipulated the participants’ blood alcohol content.
  • studies had to have assessed the participants’ intentions to engage in unprotected sex.
  • They had to have tested the association between blood alcohol content and the intention to engage in unprotected sex.
  • They had to have involved individual rather than group assessments of participants.
  • The participants had to be unaware of whether they were receiving alcohol or placebo.

What were the basic results?

The researchers found 12 studies that met their criteria. They found that the definition of intent to have unprotected sex varied between all of the studies. For example, studies asked about intention to have unprotected sex using scales ranging from 1-5 to 1-100, and differed in the number of questions they had asked the participants. The researchers found that there was an association between increase in blood alcohol content and the likelihood that the participants said they would have unprotected sex.

The researchers looked at whether there was publication bias in the studies they had included. Publication bias means that studies with certain results are more likely to be published than ones with alternative outcomes. Often this means that studies with positive results (showing an association) are more likely to be published than studies with negative results. As their assessment showed that there was publication bias, they adjusted their estimation of how alcohol affected the participants’ expression of likelihood to engage in unprotected sex. The researchers’ adjusted estimate was that an increase of 0.10mg/ml blood alcohol would result in a 2.9% increase in the participants’ likelihood of reporting that they would engage in unsafe sex (95% confidence interval 2.0–3.9%), compared with if they had consumed no alcohol.

How did the researchers interpret the results?

The researchers said that in experimental studies “there is a consistent significant effect of the level of alcohol consumption on intention to use condoms, indicating that the higher the blood alcohol content, the higher the intention to engage in unprotected sex”.

The researchers also discussed the role of personality in safe sex decisions. They said that the research had been conducted in experimental studies where people of a variety of personality types were given alcohol, and the association between blood alcohol content and likelihood of reporting intention to engage in unprotected sex remained consistent. The researchers said that this indicates that personality itself is not the sole reason why alcohol and unprotected sex are associated.


This systematic review and meta-analysis pooled the results from 12 randomised controlled studies that looked at whether there was an association between blood alcohol content (manipulated by the trial researchers) and self-reported intention to use condoms. The analysis found that for a 0.1mg/ml increase in blood alcohol content there was a 2.9% increased likelihood of participants reporting that they would be willing to engage in unprotected sex compared with participants who had consumed no alcohol.

A systematic review and meta-analysis of randomised controlled trials is a good way to assess the available evidence. This particular review used established criteria for conducting a good-quality systematic review, which is a strength of the study. The researchers were also very careful to highlight the limitations of this research:

  • Their investigation did not look at actual condom use. It would be unethical to give participants alcohol and placebo and then assess safe sex practice. Instead, they used data regarding intention to use condoms. The researchers said that in real life other factors may play a role. For example, you may ask a friend to warn you if you have consumed too much alcohol and may be at risk, or your sexual partner may insist on using a condom.
  • Although most of the studies had tried to make the experiments as realistic as possible, the setting is still experimental. The alcohol or placebo was disguised so that the participants did not know what they received. However, after a certain amount to drink, the participants may have guessed that they had received alcohol and changed their answers to the questions because of this.
  • The researchers had only made their assessments up to a blood alcohol concentration of 0.10mg/ml. They cannot be sure what the relationship between higher alcohol concentrations and likelihood of unprotected sex would be. The participants were also given experimental alcoholic drinks, and it is not clear from this research how many units of alcohol a person would need to consume to have a blood alcohol concentration of 0.10mg/ml.

Despite the limitations, the general health message of this research remains the same, and it highlights that alcohol can influence people’s decisions about whether to use a condom. Condoms are the most effective way to prevent the spread of sexually transmitted infections. A spokesperson for the Terrence Higgins Trust said that if you know you will be drinking, it is practical to carry a condom with you.

NHS Attribution