Young adults can’t buy alcohol before they turn 21, and for a very good reason: It presents health and safety risks that they aren’t ready to handle. The same can be said of cigarettes — yet tobacco is widely available to anyone 18 or over.

But that could change in Portland, where city councilors voted this week to move ahead with a proposal to raise the minimum age for buying tobacco from 18 to 21. This measure would help keep vulnerable teenagers from getting hooked and set an example for other communities, and Maine’s largest city should support it.

Youth smoking rates in Maine have dropped dramatically in the last 20 years, from 40 percent of high school students in 1997 to 12.8 percent today. But the success of tobacco-prevention efforts here shouldn’t overshadow the reality. Twenty percent of high-schoolers in our state smoke, according to the Partnership for a Tobacco-Free Maine, and each year, 2,000 Mainers under 18 become daily smokers.

Tobacco companies know that maintaining their customer base depends on getting their product into the hands of adolescents, whose developing brains predispose them to becoming addicted to nicotine and continuing the habit into adulthood. As an RJ Reynolds researcher concluded in 1982: “If a man has never smoked by age 18, the odds are three-to-one he never will. By age 24, the odds are 20-to-one.” Most underage users get tobacco through what researchers call “social sources” — family and friends who are old enough to buy. And there are plenty of high school students who are 18 and willing to purchase tobacco products for their younger friends. But that scenario is less likely if the minimum age is raised to 21.

The tighter restrictions have run into predictable opposition from tobacco retailers in the places where they’ve been implemented: the state of Hawaii and more than 100 cities nationwide, including Boston, New York and Chicago. According to doctors and public health experts, however, the short-term financial impact of the change has been overstated. They estimate that increasing the legal age for buying cigarettes will cut into total tobacco sales by 2 to 3 percent a year.

The long-term benefits, on the other hand, will be substantial. The earlier that someone starts smoking, the greater their risk of high blood pressure, asthma, heart disease, lung cancer and other disorders. The cost of treating these illnesses totals $811 million a year in Maine. So anything that discourages tobacco use will save money and lives.

While there’s nothing in the Portland proposal to keep young people from going to South Portland or Westbrook to buy cigarettes, raising the minimum age in Portland will be worth it if it keeps even one teenager from becoming addicted, and we call on city officials to embrace this measure as a step forward.