The recent Parkland shooting has gun control advocates calling for stricter laws on gun acquisition and gun features. This demand to restrict the kinds of guns that are available for civilian purchase suggests that the problem, as it is perceived by gun control advocates, is that enough of the population has dispositions that make them unable to be trusted to not misuse firearms for mass shootings. While this is no easy thesis to dismiss, there is a promising alternative explanation that deserves much more consideration than it has received: mass shootings are strongly correlated with the use of psychiatric drugs.

Many have dismissed this explanation as an unfounded strategy by gun rights advocates to divert blame for this uniquely American problem. The first thing we should note is that firearms have been widely available to Americans since before the founding of the republic. Firearms with a semi-automatic function (one shot per trigger pull) like the now infamous AR-15 have been available to the public since 1903 with the introduction of the Winchester Model 1903. But mass shootings were an uncommon occurrence. It wasn’t until the 1960s that mass shootings (defined as a public shooting spree with at least 3 fatalities, not including the gunman) began to sharply increase in frequency.

This mismatch between the widespread availability of semi-automatic rifles and the upward trend of mass shootings contradicts the theory that the widespread availability of semi-automatic rifles is the cause of the mass shootings – simply by considering that if condition A is thought to be the cause of condition B, but condition A holds for much longer before condition B finally obtains, it is very unlikely that condition A caused condition B to obtain. The same is true for those who blame mental illness full stop; it has been present for much longer than the current trend of mass shootings so what justification could we have for claiming that mental illness alone is responsible?

We can reasonably ask what set of conditions obtained in the 1960s and 70s to set off the steep rise in number of shootings. Antidepressants and other psychiatric drugs provide a solid explanation when we notice that their introduction to the US population began in the 50s and gained popularity in the 60s and 70s. In 2016, 11% of Americans over the age of 12 used antidepressants – the highest rate of any country. The possible violence-inducing side effects of antidepressants is well documented. 27 international drug regulatory agencies have documented that antidepressants can cause mania, hostility, violence, confusion, emotional blunting, and homicidal ideation. A 2015 study published in World Psychiatry journal found that users of benzodiazepines have a 45% higher chance of committing homicide. While less than 1% of the manifestation of these side effects is reported, the FDA has received, between 2004 and 2012, 14,773 reports of these side effects occurring. As of 2013, 50% of antidepressant users neglected to use the prescribed dosage. While many other developed nations have high usage of antidepressants, most of them do not have a similar access to firearms, and they have much smaller populations than the US – with a larger population comes a more frequent manifestation of adverse side effects. For example, if a side effect manifests in 1% of patients, in a population of 1 million users, we would see 10,000 manifestations while in a population of 10 million users, we would see 100,000 manifestations.

The correlation is made stronger by the fact that so many of the mass shootings in the past four decades have been committed by people with known mental illnesses and either taking antidepressants or abruptly stopping treatment (something that is strongly advised against by doctors, as it can lead to extreme psychological states including violent thoughts). It may be objected here that I am putting the cart before the horse – people with mental illnesses that may cause them to become violent are prone to taking antidepressant medication but many people take antidepressants without becoming violent. The problem with this objection is that the families of these shooters often report that their loved one became violent only after taking the medication. Also, as we’ve noted, antidepressants can and do induce violent behavior and mental illness has been co-present with semi-automatic weapons since 1903 but the increase only happened after the introduction of antidepressants.

A 2012 study found that 90% of school shooters in North America and Europe were being treated with antidepressants. The Parkland shooter was also being treated with antidepressants and it is a similar story with many of the non-school mass shooters including the Las Vegas shooter in 2017. According to WND, the vast majority of mass shooters in the past few decades are thought to have been on antidepressants.

If it is true that antidepressant medication bears the brunt of the responsibility for America’s mass shooting problem, the question remains of what we should do about it. If we assume that it is true, there are some options we have as a society:

(1) Ban semi-automatic rifles

(2) Ban those on antidepressants from owning firearms

(3) Ban antidepressants

A justification of taking options (1) or (2) would depend on whatever benefits we get from having antidepressants. We would also have to accept that we are willing to turn a significant percentage of our population into mass murdering psychopaths that will very likely look to other means for committing their homicides – or they may simply purchase their firearms illegally. A 2008 meta-analysis of antidepressant trials found that over 74 studies, it was not conclusively established that the drugs performed better than a placebo. A 2018 study of 522 trials found that overall, antidepressants performed better than placebos on those with major depression but the benefits were very short-term and modest at best. Antidepressants on those with moderate depression did not perform better than placebos but more research is needed. For a more extensive look at the ongoing scientific debate on whether antidepressants are effective at treating psychological disorders look here.

Given the lack of conclusive evidence that antidepressants benefit those with psychological disorders and the fact that they often induce violence and violent thoughts, banning weapons cannot be justified for the sake of keeping antidepressants. Banning guns independent of their relation to antidepressants is also unjustified given that both mental illness and high-powered weapons have been consistently present for much longer than mass shootings have been common. Therefore, it appears to be the case that more research needs to be done to determine whether we want to take action (3) or at least compel the medical field to be more conservative and responsible with antidepressants.