Did you know that medication can help push your blood alcohol level above the legal limit? Some people have also died because of the interaction between alcohol and a medication. For those who suffer from hay fever, mixing antihistamines and alcohol can increase the risk of an accident while driving. Alcohol can also interact with herbal products. Want to know more? Read on.

One of the most common questions that people ask their doctors at Christmas time is: 'doctor is it alright if I take a drink with this?' Given the volume of alcohol that is consumed during the festive season (and during good summer weather) it is sensible that people should ask this question.

The question also suggests that many people suspect that drinking alcohol while taking prescription drugs might not be entirely safe and that there might be potential for interaction between the two. But did you know that alcohol could also interact with many non-prescription or OTC (over the counter) products?

Let us begin our exploration by considering what happens when you swallow some alcohol. A small portion of the alcohol is metabolised or broken down in the stomach with the remaining larger portion being absorbed into the bloodstream. Most of the alcohol absorption takes place through the wall of the stomach with the remainder being absorbed in the small intestine. The alcohol is then transported to the liver through the portal vein.

When the alcohol arrives in the liver some of it is metabolised immediately with the remaining larger volume flowing on though the liver and out into the general circulation where it is distributed in various tissues of the body. The technical term of 'first pass metabolism' is used to encompass the metabolism of alcohol in the stomach as well as the breaking down of alcohol when it first reaches the liver.

The first pass concept is not just an academic one since it may have some practical consequences for some people. For example, if a small amount of alcohol is metabolised in this way then the level of alcohol in the bloodstream will be correspondingly higher. Certain medications are known to reduce the level of first pass metabolism. The list includes such drugs as aspirin and various anti-ulcer and heartburn treatments such as cimetidine, ranitidine and nizatidine. Cisapride and metoclporamide, which are also used for treating various stomach complaints, also reduce 'first pass' because they increase the speed at which the stomach empties thereby reducing the degree of alcohol being metabolised within the stomach. Erythromycin, which is a commonly prescribed antibiotic, is also known to reduce first pass metabolism. It is also important to emphasise that women metabolise less alcohol than men on first pass.

If you were taking one of these drugs and also happened to have consumed some alcohol then the level of alcohol in your blood could be higher than you might have expected. You might like to consider the sobering effect of that information if the Gardai stopped you because they suspected that you were driving a car while under the influence of alcohol. If you were taken to a Garda station to have your blood alcohol measured you might find that the level was higher than you expected. In other words the medication could have nudged your blood alcohol level above the legal limit. Try explaining that one to the judge!

Let us leave that sobering scenario and return to a consideration of how the body deals with the alcohol you have consumed. As most people know the liver is the major organ in the body for breaking down alcohol. Several enzymes are responsible but the two most important enzymes for alcohol metabolism are known as ADH (alcohol dehydrogenase) and cytochrome P450. ADH converts alcohol into acetaldehyde, which is one of the principal culprits in producing the hangover effect. The level of activity of these two enzymes can vary greatly from person to person. This may explain why some people are able to drink large amounts of alcohol and never appear to suffer from a hangover. They may simply be metabolising more alcohol through the cytochrome P450 system, which does not result in unpleasant hangover symptoms.

Cytochrome P450 is the key enzyme involved in interactions between alcohol and medication. Alcohol can either increase or decrease the level of metabolism of drugs by this enzyme. For example the alcohol could increase the level of the drug in the bloodstream because the alcohol had reduced the level of cytochrome P450 activity. In other words if the enzyme is not breaking down the alcohol quickly enough more of it is left circulating in the bloodstream, which could have serious consequences. In that scenario the person is effectively overdosing on the medication because of the alcohol’s effect. This is the process at work when people drink alcohol when taking warfarin, which is a frequently prescribed anticlotting drug. This could have very serious consequences and result in reduced clotting ability in the blood, which increases the tendency to bleed. The consequences could range from a minor nosebleed to a major internal haemorrhage. People have died because of this interaction between alcohol and warfarin.

Paradoxically if the person on warfarin happens to be a very heavy drinker then the level of cytochrome P450 activity is already high because of their drinking and this can reduce the level of warfarin in the bloodstream. This effect then requires that the person be prescribed much higher doses of warfarin in order to achieve the desired clotting levels in the blood. It is clear that drinking alcohol while taking warfarin is potentially very dangerous.

Alcohol can affect the metabolism of several drugs other than warfarin. The list includes barbiturates, which were formerly prescribed as sedatives but are still frequently used today in the control of epilepsy. Alcohol consumption can affect seizure control in epileptics. Young people with epilepsy may drink as their friends do and experience an unacceptably high number of fits due to the interaction between alcohol and the barbiturates. Alcohol can also increase the rate of phenytoin breakdown, which is another drug used to treat epilepsy. The cytochrome P450 system is centrally involved in both these interactions.

There is one situation where the interaction between alcohol and a drug is used for positive benefit. I am referring to the use of disulfiram in the treatment of alcoholism. Disulfiram is prescribed to some alcoholics to discourage them from drinking alcohol. If an alcoholic drinks alcohol while taking disulfiram he or she can become acutely ill with severe generalised flushing all over the body. Some alcoholics are enabled to maintain sobriety by using this drug. However, several other drugs can produce this disulfiram-like effect when alcohol is consumed. The list includes such drugs as the painkiller phenacetin, antibiotics such as nitrofurantoin, cephalosporins and metronidazole, anti-angina medication such as nitrates and various diabetic drugs including chlopropamide and tolbutamide.

Anti-inflammatory painkillers are widely used and they are available both on prescription and as OTC products. One of the principal side effects of these drugs is gastric bleeding. This side effect is considerably enhanced when alcohol is consumed, which makes it a very bad idea to take an anti-inflammatory painkiller in an effort to prevent a hangover headache. This effect occurs with a long list of products but two of the most important are aspirin and ibuprofen, which are available in many households and are commonly used as general painkillers.

One very important interaction that I should mention is the interaction between alcohol and antihistamines. Many people will be using these products over the coming weeks as the hay fever season arrives. Alcohol can increase the level of drowsiness that is associated with the use of these drugs. It can also affect concentration and reaction times. It is not overstating things to say that drinking alcohol while using antihistamines could increase your chances of having an accident while driving. When using antihistamines you should seek a drug that is non-sedating. These newer antihistamines have not been documented as having this particular interaction with alcohol.

Drowsiness can also be a significant problem when using sleeping tablets, sedatives and tricyclic antidepressants. Alcohol can markedly increase the level of sedation caused by these drugs. In the case of tricyclic antidepressants alcohol can also lower the blood pressure giving rise to feelings of lightheadedness and may even cause fainting. The interaction between alcohol and these drugs can lead to unconsciousness and even death. This is a particular worry in the case of a deliberate overdose. It is possible for a person to take a sub-lethal dose of these medications only to die because of the enhancement of the drugs sedative effect from drinking alcohol.

Alcohol can also interact with a wide variety of herbal products. Many people assume that just because a product is described as natural or herbal that it is perfectly safe and cannot interact with other products. This is patently untrue and there are now many examples of alcohol interacting with herbal products. For example, echinacea, camomile and valerian can cause sedation and drowsiness when a person drinks alcohol.

Having described the various types of interaction that can occur between alcohol and drugs I want to conclude with a simple and clear message. Always read the product label when taking a prescription or OTC medication. Specifically check for any mention of possible interactions with alcohol. Don’t assume that a product is inherently safe just because it is described as OTC or herbal. Finally, the question 'doctor is it alright if I take a drink with this' should be a question for all year round and not just during festivities.