President Trump has spoken out forcefully about defeating the illegal drug problem—as powerfully as any recent president, including Ronald Reagan. Now he is urged to support marijuana legalization in the midst of the most deadly drug abuse epidemic in American history. President Trump should refuse—it’s a bad deal with unsustainable consequences.

Obviously, decriminalizing the sale and possession of marijuana will make the drug more available and increase use. The advocates of decriminalization contend, however, that the harm of more use is less than the harm caused by current law and its enforcement. This is ridiculous.

First and foremost, marijuana is already associated with more abuse and dependency (now called substance abuse disorder) than all other illegal drugs combined. Roughly four out of seven problem users of illegal drugs are using marijuana. This is a dangerous blind spot exploited by many legalization advocates (although some of them are now warning about the growing risk of heavy marijuana use under legalization).

If you doubt legalization brings a rapid increase in marijuana use and addiction, consider the situation in Colorado. This is the test case; the experiment in legalization created by the Obama Administration. Colorado permitted the so-called “medical” sale of marijuana in 2009 and “recreational” sale in 2013. Some seem to believe, falsely, that marijuana use in Colorado has been accompanied by a decline in other drug use. This is emphatically not true. Last year more Coloradans died from drug overdoses than at any time in the state’s history. The cruel “Colorado experiment” has failed. Nonetheless, legalizers want to repeat it from sea to shining sea.

Second, marijuana use is not safe. Legalization advocates frequently play on the fact that many Americans have used the drug without recognizable harm as proof that most marijuana use is benign. We are all victims of our experience. The genuine research points to massive ignorance about the known dangers.

As the American Academy of Pediatrics notes: “The adverse effects of marijuana have been well documented” and include “impaired short-term memory, decreased concentration, attention span, and problem solving” which “interfere[s] with learning.” Researchers have also reported: “Regular cannabis use in adolescence approximately doubles the risks of early school-leaving and of cognitive impairment and psychoses in adulthood.” And other researchers have warned that States that have legalized “medical” marijuana find an association with higher 12th grade drop-out rates and lessened college attainment.

There is no known, safe level of marijuana use. And the highly concentrated forms of cannabis brought to the market in recent years probably increase all the known harms of marijuana use.

But the most troubling research has found: “Persistent adolescent-onset cannabis users” showed “an average 8-point IQ decline from childhood to adulthood.” Marijuana use can permanently lower intelligence and worsen, perhaps cause, serious mental illness. As the Journal of the American Medical Association has reported: “There is little doubt about the existence of an association between substance use and psychotic illness…studies suggest that the association between cannabis use and later psychosis might be causal, a conclusion supported by studies showing that cannabis use is associated with an earlier age at onset of psychotic disorders, particularly schizophrenia.”

The science warns that marijuana use makes you less intelligent and can bring on serious mental illness. There is no known, safe level of marijuana use. And the highly concentrated forms of cannabis brought to the market in recent years, probably increase all the known harms of marijuana use.

Finally, marijuana is the gateway to greater drug use and for more and more Americans that means early death. Not all marijuana users turn to opioids, cocaine, meth, and other drugs of abuse, but many of them do and each year, tens of thousands of those who move on to other drugs die of overdoses. Such deaths topped 60,000 in 2016, increasing over 20 percent in one year. Substance abuse is additive, not self-limiting. More marijuana users means more users of other drugs—more addiction and more overdose deaths.

President Trump is being asked to expand vastly the marijuana gateway to addiction and death as opioid supply increases, the meth supply is growing, and the supply of cocaine is at record levels. This can only push the historic overdose death rates to staggering new levels.

The President should forcefully reject marijuana legalization. He should direct his staff to get the facts out and push back against the ignorance that risks turning our drug policy into one of the worst self-inflicted wounds in American history.

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William J. Bennett was secretary of education for President Ronald Reagan and former director of drug control policy for President George H.W. Bush. John P. Walters is Hudson Institute’s chief operating officer and former director of drug control policy for President George W. Bush.