Economist Marina Adshade is the author of The Love Market: What You Need to Know About How We Date, Mate and Marry. She teaches at the University of British Columbia's Vancouver School of Economics and SFU School of Public Policy. Niko Bell is a journalist who writes on sexual health and the science of sexuality.

Sixty-one per cent of Canadian women have had an unintended pregnancy, notes a study by Canada's Society of Obstetricians and Gynaecologists. Government policy is to blame.

On Jan. 1, the B.C. government joined Ontario and Quebec in offering coverage of a drug that prevents HIV infection for people at high risk. This is a smart move, spending a little money on prevention to save much more on health care down the road. If only the provinces were as clever when it came to providing affordable contraceptives for women; failing to do so costs taxpayers millions of dollars and imposes undue hardship on parents and children.

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Canada is one of the only countries with publicly funded health care that doesn't provide some contraceptive coverage for women. And there is ample evidence that providing free contraceptives leads to a dramatic drop in unintended pregnancies, teen pregnancies and abortions.

The logic of paying for HIV prevention drugs and contraceptives is strikingly similar. Both put the right tools in the hands of vulnerable people to make good decisions about their sexual health, saving themselves from needless suffering and society from unnecessary downstream costs.

Pre-exposure prophylaxis, a drug combination shown to be as effective as condoms for preventing HIV, will likely cost the B.C. government a little over $2,000 a year per user. The BC Centre for Excellence in HIV/AIDS expects up to 5,000 of the highest-risk British Columbians, mostly gay and bisexual men, to take it. Each HIV infection it prevents will save the health-care system from a lifetime of drug costs, as well as potential new infections down the line.

But if an ounce of HIV prevention is worth a pound of cure, an ounce of long-term birth control for women is worth a ton.

The Mirena hormonal IUD, for example, costs about $350, and provides protection from unwanted pregnancy for seven years. In contrast, a single abortion, about 100,000 of which are performed in Canada every year, costs the taxpayer somewhere in the region of $750. That's enough money spent on abortions to place over 200,000 new long-lasting IUDs every single year; over the next five years that would provide an IUD to every adult woman under 24. And that disregards the governments' ability to negotiate lower prices from pharmaceutical companies when buying in bulk.

Here in Canada, we're used to feeling smug about our socialized medical system, but it's American examples that show how effective free contraceptives can be. Since Colorado started offering free or low-cost access to IUDs in 2009, the teen birth and abortion rate has fallen by half. The state spent a $28-million philanthropic grant over eight years providing contraception, and is estimated to have saved $70-million in medical and social costs. Another study estimated that every dollar spent in Colorado on IUDs recouped $5.85 on medical costs alone.

Arguably, there are more important costs to unintended births than those represented on budget lines. Women who experience unplanned births are more likely to suffer physical abuse and mental-health issues, and less likely to find themselves in long-term romantic relationships. The children born to mothers who would have preferred to at least delay their pregnancies are more likely to have poor physical and mental health, less likely to finish high school and more likely to be involved in the criminal justice system as teenagers. Even the siblings of those children suffer poorer outcomes than those whose mothers were able to choose the timing of their births.

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And for those concerned, there is no evidence that access to birth control will attenuate births to Canadian women; other countries with free contraceptives have higher birth rates than Canada, not lower. Women who have access to free contraceptives simply postpone having children until they are ready.

Tuesday, B.C. also took the long-overdue step to cover the pregnancy-termination drug Mifegymiso. Provinces must go further. There is an overwhelming economic and public-policy case for paying for women's contraception, even aside from the moral imperative to improve outcomes for mothers and children and empower women to make their own reproductive choices.

On the campaign trail to B.C.'s last provincial election, NDP Leader John Horgan said, of HIV prevention drugs: "Give people the medical devices that they need to protect themselves, and you're going to reduce costs over time."

Mr. Horgan is right, and now he should heed his own words when it comes to contraceptives for women, where they are doubly true.