If used early in the course of illness, participants who used zinc under their tongue or as a nasal spray 1.8 times more likely to recover before those who used a placebo.
…..webmd.com, Does Zinc Really Help Treat Colds?, Lindsay Kalter, 2021
On the downside, there were more side effects among those who used zinc, including nausea or stomach upset, mouth irritation, or soreness from lozenges. The risk for a serious problem, such as loss of smell or copper deficiency, was low.
Source: https://www.webmd.com/cold-and-flu/news/20211109/does-zinc-help-treat-colds