The FDA has issued another warning about the herbal supplement kratom, this time noting that unsafe levels of heavy metals have been found in 30 products in analyzed.

The latest warning is not the first one on the heavy metals issue. Back in November, the FDA issued a similar warning. Last week’s announcement made by the agency was many of final results of its analysis.

People that use kratom regularly may expose themselves to higher than normal levels of nickel and lead, the FDA notes. A person that uses kratom over the long term, as a result, could develop heavy metal poisoning, which could lead to anemia, high blood pressure, kidney damage and even some cancers.

People who use kratom say it can treat a variety of conditions, including pain, depression and for opioid withdrawal. The FDA, however, says that there is no approved use for the herb. In addition, last summer, the FDA reported an outbreak of salmonella connect to kratom products and noted that it has opioid-like qualities and can be potentially addictive. It has also been linked to a number of deaths.

“The findings of identifying heavy metals in kratom only strengthen our public health warnings around this substance and concern for the health and safety of Americans using it,” former FDA Commissioner Scott Gottlieb said in a statement.