20.02.2021 |

Episode #5 of the course Introduction to drugs and behavior by Dr. Daniel McGrath


Quick, name the most harmful drug in the world. Is it heroin? Cocaine? Methamphetamine? All of these drugs are very destructive and have high mortality rates, but when all societal harms are considered, alcohol likely takes the top spot as the most harmful drug of abuse. David Nutt, Professor of Neuropsychopharmacology at Imperial College London, led a high-profile study to identify the most harmful drugs in the United Kingdom (Nutt, King, & Phillips, 2010). The assessment was published in the Lancet, and included numerous harms to oneself and others. Examples include damage to health, impairment, dependence, mortality, harm to the community, among several others. The research team combined these harms and developed an overall “drug harm score” totaling up to 100. Alcohol achieved a total score of 72, whereas heroin (in second place) was given a 55 and crack cocaine a 54.

Human beings have been consuming alcohol for thousands of years. The type of alcohol that people drink is ethyl alcohol. It is created through the process of fermentation, which occurs when yeast converts sugars found in grains or fruit (e.g., grapes) into alcohol and carbon dioxide molecules. Humans also discovered that heating fermented alcohol creates beverages with higher alcohol content such as rum, a process called distillation. The alcohol content is referred to as “proof”, which is twice the percentage of alcohol in a beverage. For instance, 80 proof means that a bottle of rum is comprised of 40% alcohol.

Alcohol is almost exclusively consumed through oral administration. When we drink alcohol, it enters the stomach where a small amount (~10%) is absorbed into the bloodstream through the stomach lining. A lot of alcohol molecules are also broken down and metabolized. The remaining alcohol passes into the intestinal tract, but how quickly this happens depends on whether the person has eaten recently. Food will slow the process and aid in metabolism, whereas drinking on empty stomach results in faster absorption. Once in the small intestine, alcohol diffuses through the gastrointestinal wall and enters the blood.

Blood alcohol concentration (BAC) is how we measure the amount of alcohol in a person’s system. This is what is measured with a breathalyzer test. BAC is milligrams (mg) of alcohol per 100 milliliters (ml) of blood. For example, a BAC of 0.05% would be 50 mgs of alcohol per 100 ml of blood. In many jurisdictions, a BAC of 0.05% or 0.08% is the legal limit for impaired driving. A BAC of 0.40% or higher can be fatal. Reaching a certain BAC depends on many factors such as gender, age, weight, experience drinking (tolerance), medications, and types of mixer used in a drink. The liver metabolizes alcohol at a rate of about one standard drink per hour; as such, it can take several hours to sober up after drinking. Interestingly, alcohol does not have a half-life; this is a topic that will be addressed in the next lecture.

Once in the blood, alcohol is carried to the brain. The neuropharmacology of alcohol is quite complex, but the gist of it works like this. Alcohol binds to several receptors in the brain. In particular, it binds to GABA receptors. GABA is the principal inhibitory neurotransmitter in the brain, which means it generally decreases neural activity. Therefore, alcohol mimics GABA and leads to the sluggishness and tiredness associated with drinking. It also reduces glutamate, an excitatory neurotransmitter, which further contributes to feelings of tiredness. Lastly, alcohol consumption leads to increases in dopamine, a process that contributes to alcohol addiction.

Acute effects. Alcohol can have numerous acute effects, especially after heavy drinking. These effects are biphasic, meaning that low doses create a feeling of excitement and euphoria, but when doses get larger, the effects are sedation and feeling depressed. Most cognitive functions are impaired while intoxicated. Vision, smell, and taste are all dulled. Memory formation, in particular, is strongly affected with blackouts being common after binge drinking. This could be where the drinker remembers fragments of the evening or entire blocks of time are missing. In terms of harm, reduced executive functioning can lead to a number of poor decisions, including driving while intoxicated.

Chronic effects. Alcohol can result in serious long-term effects as well. Roughly 5-10% of alcoholics will go on to develop cirrhosis of the liver, a serious and often fatal ailment. Heavy alcohol use is a considerable risk factor for cancer, especially cancers of the esophagus, liver, breast, and colon. Lastly, alcohol is a very serious teratogen, which refers to a substance that can lead to birth defects. Specifically, fetal alcohol syndrome is a severe life-long developmental disorder that can occur in infants of mothers who drink during pregnancy.

Addiction potential. Alcohol use is pervasive in most countries; not surprisingly, rates of alcohol use disorders or alcoholism are also high. Approximately 10% of Americans have an alcohol problem, with rates of recent binge drinking being two to three times higher than that. Alcohol increases dopamine transmission in the reward system and, therefore, can lead to potential addiction. Furthermore, there is a strong genetic component, with alcoholism tending to run in families. Numerous treatments are available, including psychotherapy, several medications such as naltrexone, and support groups like Alcoholics Anonymous.

In tomorrow’s lesson, we are going to cover another common drug of abuse, nicotine and tobacco. See you then!


Recommended book

Drink? The New Science of Alcohol and Your Health by David J. Nutt


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