Years ago, a friend found his mother in the hot tub, pale and not breathing. Next to her, a glass of red wine and a bottle of the prescription anti-anxiety medication she took each night before bed. A similar combination of substances and circumstances is believed to have killed singer Whitney Houston.

Alcohol is relatively safe when consumed responsibly and in moderation. It effects are more complicated — and dangerous — when taken in excess or combined with other substances.

When mixed with sedatives, individuals who drink may experience severe drowsiness, loss of coordination, and difficulties breathing.

Nearly three out of four American adults drink alcohol. Although drinking is known to pose risks when combined with certain prescription medications, there are few studies on the use of these alcohol-interactive (AI) medications.

But a new study from the National Institute on Alcohol Abuse and Alcoholism offers an estimate of the proportion of adult drinkers who use any of the variety of prescription medications with the potential to interact with alcohol. They can cause adverse reactions ranging from nausea or headaches to internal bleeding or death.

The research team expected to find that this problem was largely restricted to elderly individuals, based on prior studies, since as we age, our bodies break down both alcohol and medications less efficiently, meaning these substances can stay in the blood stream for longer periods of time, thereby increasing the likelihood of an interaction.

“People develop more chronic diseases as they age,” an author of the study, Rosalind Breslow, said in a statement. “So older people are more likely to be taking medications, many of which can interact harmfully with alcohol. They also may be taking a number of medications to treat multiple diseases.”

A staggering 78 percent of seniors combined alcohol with medications that can interact harmfully with alcohol.

The study relied on more than a decade of data gathered on 26,000 adults in the National Health and Nutrition Examination Survey.

Roughly 42 percent of drinkers in the US used one or more alcohol-interactive prescription medications, researchers found. A staggering 78 percent of seniors combined alcohol with AI medications. These commonly included blood pressure medications, sleeping pills, pain medications, muscle relaxers, antidepressants, antipsychotics and medications for diabetes or cholesterol.

“Our findings highlight a major gap in the literature,” Breslow added. The team found that there were no nationally representative data in the United States that examined the use of alcohol with a wide range of prescription medications, and yet “it appears that a large percentage of people who drink regularly could be at risk of serious alcohol and medication interactions.”

Alcohol consumption can interfere with or intensify the effectiveness of these medications. For example, alcohol can increase blood pressure, which is counterproductive if someone is taking medications to control their blood pressure.

Mixing alcohol, which has a diuretic effect (that is, increases urine output), could lead to dehydration in individuals already taking diuretic medications. When mixed with sedatives, individuals who drink may experience severe drowsiness, loss of coordination, and difficulties breathing.

The authors conclude that individuals receiving AI, particularly the elderly, should be educated by healthcare providers about the risks of combining alcohol with their medications. The study also underscores the importance of being honest with your physician regarding your drinking habits.

The findings are published in Alcoholism: Clinical & Experimental Research.