High-concentration cannabis products, while often legal, may be riskier than they appear.

A sweeping look at nearly 100 previous studies shows strong links between psychosis, schizophrenia and cannabis use disorder and high-concentration cannabis products.

The worrisome compound is THC, which is short for delta-9-tetrahydracannibinol [tetra-hydra-kuh-nab-buh-nuhl]. It is the ingredient in cannabis that makes those who smoke, eat, vape or otherwise ingest it feel high.

High-concentration cannabis products are now legal in more than half of the United States.

Generally, high-THC content is defined as 20% or higher for dried cannabis flower and up to 50% or more for concentrates, which are often called “wax,” “shatter” or “dab.”

Even states that only allow medical-use marijuana typically allow some high-concentrate THC products. The researchers chose studies of THC concentrate products that exceeded 5 milligrams or 10% THC per serving, or were labeled high concentrate, shatter or dab.

The University of Colorado-led researchers analyzed 99 studies completed between 1977 and 2023.

The team found strong links between the use of high-concentration THC products and psychosis, cannabis use disorder and schizophrenia.

In the studies that were not testing ways to use cannabis as a medical treatment, 53% identified negative associations with anxiety.

Among studies that tested cannabis as a treatment, results were mixed.

The bottom line: The findings bolster previous studies that found negative mental health issues connected with higher THC concentrations. Unfortunately, the researchers say they need more evidence before giving patients firm advice.