If California approves Proposition 64 next week, it is likely to create significant momentum toward legalizing marijuana throughout the U.S. and beyond. The results of the election may signal the birth of a massive new “vice” industry along the lines of the tobacco and alcohol behemoths.

Marijuana prohibition has a sorry history. Early anti-marijuana laws were based far too much on bigotry and hypocrisy and far too little on evidence and reason. In the past, marijuana sanctions were so severe they were unwarranted under any principled theory of criminal justice. More recently, the laws have been used as a pretext for biased law enforcement, targeting young men of color. And because of prohibition, U.S. marijuana sales have helped to finance brutal drug traffickers who are destabilizing Mexican society.

At the same time, legalization will pose its own problems.

The experiences of Colorado and Washington state — where legalization went into effect in 2014 — ought to give Californians a preview of what to expect if Proposition 64 passes. Unfortunately, it will be several more years before we have enough data to credibly assess the effects in both those states.

In the meantime, we can look to some potentially relevant cases for clues. My colleagues and I have studied Dutch cannabis “coffee shops,” medical marijuana policies and the decriminalization of possession in various states, and the regulation of tobacco and alcohol around the world. We have built simulation models of the cannabis economy, and tested the effects of various assumptions about how sellers and buyers will behave. Our work can’t forecast what will happen after legalization, but it does suggest some of the variables that will be in play.

Legalization will have two different kinds of effects and they may push in opposite directions.

First, legalization is likely to reduce the average harm per dose of marijuana. Some of these reductions will be pharmacological: the result of better quality control and predictability in the legal production of the drug. Other reductions will be sociological or political: less government intrusion in people’s affairs, fewer arrests, a minimized black market.

But legalization can also be expected to increase the number of doses consumed, simply because it will be easier to obtain. In the end, total harm related to marijuana could rise even if the average harm per dose falls.

One way legalization will affect use is through aggressive commercial promotion. We are already seeing marijuana-related billboards on California freeways, and Colorado has struggled to discourage the brightly colored marijuana candy shapes and packaging that can be as enticing to children as it is to their parents.

It is possible to legalize marijuana without commercialization. Voting for Proposition 64 would be far less consequential if the measure allowed for home cultivation, not retail sales (as in Washington, D.C.), or if consumers had to join nonprofit co-ops in order to purchase marijuana (as in Spain). But those options aren’t on our ballot—64 establishes commercialized, for-profit marijuana sales in California.

Cost will play an important role in legalization’s effects. Under prohibition, prices are inflated by artificial scarcity and the need to compensate dealers for their legal risks. With legalization, there will be economies of scale in mass production, and competition could shave profit margins razor thin. Prices will fall, we just don’t know how far. Studies show that marijuana users, like consumers of other drugs, are sensitive to cost; they buy more when prices go down, and cheaper marijuana may also attract new users and perhaps younger users.

The effect of legalization on potency is another important question. The trend under prohibition has been rising potency. Will cheaper, more readily available marijuana decelerate or accelerate the production of stronger strains? If potency continues to climb, many experts believe it will carry increased public health dangers.

Finally, will increased marijuana use lead to reductions in alcohol consumption? If it does—and it is a big if—from a public health standpoint that might be a fair trade because alcohol impairment carries enormous and well known costs. But if alcohol and marijuana are not substitutes for each other, we’ll just end up with more intoxication than we had before.

In general, for states that decide to legalize marijuana, the sky isn’t going to fall. California’s already relatively lenient marijuana laws mean the changes brought on by legalization won’t be as radical as they might have been otherwise. And the prevalence of marijuana use would have to almost double before we reach the historical peak levels of the late 1970s, and the nation seems to have survived that.

Proposition 64 could launch a major new industry, and if mass production, lower prices and aggressive promotion in fact encourage more marijuana users, using more often, and in larger quantities, there will be health and safety consequences we don’t yet fully understand. No one should have illusions that this is no big deal.

Robert MacCoun, James and Patricia Kowal Professor of Law, is a social psychologist and public policy analyst. He is co-author (with Peter Reuter) of “Drug War Heresies: Learning from Other Vices, Times, and Places.”

This op-ed was originally published by the Los Angeles Times on November 3, 2016.