FATAL CONNECTION. The percentage of smokers (gray bars) who are alcoholics or alcohol abusers far exceeds the number of nonsmokers who are (black bars). The pattern holds true for other drugs of abuse.

Nicotine and alcohol. Two simple organic molecules that share similar attributes: they produce a high, and they are highly addictive. In addition, both exact an enormous toll in human suffering, mortality and medical costs.

Last July, the National Institute on Alcohol Abuse and Alcoholism estimated that alcohol is implicated in as many as 44 percent of the more than 40,000 annual traffic crash fatalities. Liver cirrhosis, although on the decline since 1973, remains the 11th leading cause of death. And tobacco use, the number one preventable cause of death in the United States, claims more than 400,000 lives and $50 billion in direct medical costs each year, according to the Centers for Disease Control and Prevention. Lung and heart diseases are the principal killers, but smoking contributes to a broad range of other maladies.

The good news is that scientists may be able to take advantage of another trait these "everyday" drugs share to render them less harmful. Research shows that alcohol and nicotine--as well as coffee and sweets, for that matter--become habit-forming in like ways. All overstimulate the brain's so-called reward system, as do the major drugs of abuse, such as cocaine and heroin.

This network of neurons, a circuit running through the ventral tegmental area (VTA), the nucleus accumbens and the prefrontal cortex, is normally activated when an animal does things--such as eating or sex--that help it to survive. This activity increases levels of sundry neurotransmitters, such as dopamine and seratonin, inducing pleasurable feelings. Most drugs overactivate the circuit, so that addicts in danger will often turn to one or several subtances instead of self-preservation.

Numerous studies have suggested a common link in addiction by showing that people addicted to one substance are more likely to be addicted to others. The strongest connection is between tobacco and alcohol. Smokers drink twice as much alcohol as non-smokers--and their risk of drinking too heavily is also twice that of non-smokers. One study found that alcoholism is 10 to 14 times more prevalent among smokers. And, while the percentage of smokers has dropped to 30 percent of American adults, it is unchanged among alcoholics. In addition, smokers are more likely to take illicit drugs than non-smokers are. In 1995, 13.6 percent of smokers were illicit drug users, compared with only 3.0 percent of non-smokers.

In fact, alcoholics are more likely to die from the effects of smoking than from those of alcohol. The Mayo Medical Center in Rochester, Minn. examined the 197 traceable deaths out of 845 patients admitted to its addiction treatment program between 1972 and 1983. The researchers found tobacco-related causes in 85 deaths (43 percent) and alcohol-related causes in 55 deaths (28 percent).

To be sure, beating either habit is hard, let alone both--and many people replace one for the other. The National Treatment Improvement Evaluation Study (NTIES), a Congressionally-mandated five-year study, found that whereas many clients served by federally-funded programs cut their drug use in half up to a year after treatment, many eventually relapsed. And although there is now one non-smoker for every smoker in the U.S., most treatment programs report success rates of less than 10 percent after one year.

But new medications for both nicotine addiction and alcoholism are on the way, now that scientists realize that addictions stem from much more than "an addictive personality" or weak will. The remedies being tested actually target the cascade of neurochemical events at the root of addicts' cravings. Isradipine, a drug recently shown to reduce the desire for alcohol, is a calcium-channel blocker normally used to treat high blood pressure. The compound also appears to affect levels of dopamine in the brain's reward center. Similarly, a prescription antidepressant called bupropion seems to block smokers cravings by mimicking nicotine's ability to increase the amount of dopamine in the brain.

Although a drug that would treat all addictions is still a long way off, the new research is already having an impact on the way addiction is medically managed. Many treatment centers, such as the one at the University of Texas Medical School, are now taking a holistic approach. Alcoholics entering inpatient programs don't just give up alcohol--they part with their cigarettes and coffee as well.

Treating multiple addictions at once does not seem to make recovery any more difficult. The Texas center reports that since it became "smoke free" in 1991, it has observed no change in the rate of premature discharge, in the percentage of people who completed the program and in patient stress or unusual incidents. "It turns out it's not that hard to wean people from nicotine when it becomes the expectation of the program," say Terry Rustin, who heads the unit.

Even so, some researchers question whether treatment can ever overcome behaviors heavily reinforced by evolution. Randolph Nesse and Kent Berridge, psychiatric investigators with the Institute for Social Research at the University of Michigan in Ann Arbor, reported in Science that medicine may never win the war against drug addiction because "it is rooted in the fundamental design of the human nervous system."

Until proven otherwise, many scientists hold out hope.