An analysis of the videos served to these accounts found that through its powerful algorithms, TikTok can quickly drive minors—among the biggest users of the app—into endless spools of content about sex and drugs.

TikTok served one account registered as a 13-year-old at least 569 videos about drug use, references to cocaine and meth addiction, and promotional videos for online sales of drug products and paraphernalia. Hundreds of similar videos appeared in the feeds of the Journal’s other minor accounts.

TikTok also showed the Journal’s teenage users more than 100 videos from accounts recommending paid pornography sites and sex shops. Thousands of others were from creators who labeled their content as for adults only.

Still others encouraged eating disorders and glorified alcohol, including depictions of drinking and driving and of drinking games.