In a world where reason has been suspended in favor of lunatic fads, the use of cannabis has gained more traction than a football field sized stretch of flypaper. It has been used for a variety of medical conditions such as nausea, as an appetite stimulus for patients with AIDS, and for pain relief. Twenty one states, and counting, have legalized the recreational use of the drug in various forms. There are several reasons for such action.

A lot of people have been jailed for selling the stuff, far fewer for mere possession. Given the difficulty governments have had preventing the sale, distribution, and use of drugs that have lethal side effects it does not seem reasonable to imprison thousands of Americans for marijuana dissemination or use. Especially, as many think the drug has little or no ill sequelae.

States believe they can generate sizable amounts of tax revenue from the lawful use of cannabis. This revenue has proved to be less than anticipated as marijuana is so easy to grow in large amounts such that illegal sellers can offer the stuff at a lesser price than the lawful sale by escaping the tax regime.

The question addressed here is how safe, or unsafe, is prolonged cannabis use? We don’t have a lot of data addressing this question, but a good guess would be that ingesting or inhaling a mind altering drug frequently for prolonged periods will have serious deleterious consequences.

Medical use of cannabis containing drugs can prove very profitable for pharmaceutical companies. Yet the FDA has only approved Epidiolex, which contains a purified form of the drug substance cannabidiol, for the treatment of seizures associated with Lennox-Gastaut syndrome or Dravet syndrome in patients one year of age and older. Nabiximol’s (trade name Sativex) is a specific cannabis extract; it was approved by Health Canada for prescription for certain types of pain – specifically central neuropathic pain in multiple sclerosis, and the treatment of cancer pain unresponsive to optimized opioid therapy. Persuasive evidence for the effective medical use of cannabinoids is so far lacking. The efficacy of cannabinoids for the treatment of pain is likely low and the side effects of its use are likely serious – see below.

A new generation of cannabis products has exploded onto the scene, driven by marketing that fuels a multibillion-dollar industry. The average content of THC (tetra-9-tetrahydrocannabinol, the psychoactive and potentially addictive chemical in cannabis) in smoked whole-plant products has risen from one percent to four percent in the 1970s to 15 percent to 30 percent from today’s cannabis dispensaries. Edibles and vapes may contain even higher concentrations of THC.

Thus, we are faced with a new potentially serious problem. The widespread use of cannabis for purely recreational reasons in doses previously unavailable has unknown side effects. A long term study of cannabis usage from New Zealand (at lower doses than now likely to be employed) showed that

 IQ declined from childhood to midlife (mean=−5.5 IQ points), poorer learning and processing speed relative to subjects childhood IQ, and informant-reported memory and attention problems. These deficits were specific to long-term cannabis users because they were either not present or were smaller among long-term tobacco users, long-term alcohol users, midlife recreational cannabis users, and cannabis quitters. Cognitive deficits among long-term cannabis users could not be explained by persistent tobacco, alcohol, or other illicit drug use, childhood socioeconomic status, low childhood self-control, or family history of substance dependence…Research is needed to ascertain whether long-term cannabis users show elevated rates of dementia in later life.

In addition to the effect of marijuana on cognition, the effect of inhaling heated smoke from a joint on the lungs is not known. It can’t be good. The occasional use of cannabinoids for recreation is likely to be no worse than an occasional cigar or a snifter of fine brandy. Like the rest of life good judgement, if it can be found, will point one in the right direction.