Fear is overcoming reason as the threat of the coronavirus spreads.

After hearing President Trump say, without scientific evidence, that the antimalarial drug chloroquine could be a “game changer” in the fight against Covid-19, an Arizona man died and his wife was left in critical condition after they swallowed a form of the chemical used to clean fish tanks called chloroquine phosphate.

The same day, a government official reported that three men in Nigeria had overdosed on chloroquine, and warnings against taking this medicine were made public.

As physicians, our advice is based on medical evidence that weighs the benefits of a medicine or treatment against its potential harms, such as a medication’s side effects or a surgical procedure’s complications. This rigorous decision-making is backed by research from peer-reviewed clinical trials, and is subject to government oversight. It’s dangerous for people with no medical license or training or understanding of science to promote the effectiveness of unproven treatments.

The efficacy of chloroquine and its derivatives deserves rapid scientific study, and, rightly, there are ongoing clinical trials. However, the off-label use of these medicines against Covid-19 outside of a monitored clinical trial and without proper cardiac testing, could cause an abnormal heart rhythm and even death. These medications are also used in the long-term treatment of other medical conditions, including lupus and rheumatoid arthritis, and increased use against Covid-19 may lead to shortages for those who need it chronically.