Fenproporex is a central and indirect-acting sympathomimetic. It was developed as an anorectic drug. Their anorectic effects are believed to be a result of adrenergic activation. Fenproporex has never been approved by the US Food and Drug Administration (FDA) for sale in the US due to lack of efficacy and safety data. There is a paucity of randomized, placebo-controlled trials on Fenproporex. These studies suggest that Fenproporex is modestly effective in promoting weight loss. Data from these studies are insufficient to determine the risk-benefit profile of Fenproporex. Abuse potential and amphetamine-like adverse effects are causes for concern. Adverse effect most frequently reported are: insomnia, anxiety, depression, irritability, dry mouth.

Fenproporex:
https://drugs.ncats.io/drug/W0194S5FOA

Americans who use illegal diet pills from South America are taking amphetamines without knowing it and seriously risking both their health and their jobs. Although the US Food and Drug Administration (FDA) has banned the majority of amphetamine-based appetite suppressants, many are still prescribed in other parts of the world, including South America. The second most often prescribed amphetamine-based appetite suppressant worldwide is fenproporex. It is known to be addictive and is rapidly converted into amphetamine in the body. The international availability of fenproporex, combined with Internet sales and other illegal markets, have led to its availability in the US, despite an FDA ban. Most physicians in the US are unaware of the existence of these diet pills combining fenproporex and benzodiazepines, selective serotonin reuptake inhibitors, diuretics, laxatives, thyroid hormones and other substances.

Excerpt from medicalxpress.com:
https://medicalxpress.com/news/2009-01-caution-weight-imported-diet-pills.html

Fenproporex is an amphetamine based anorectic which is rapidly metabolized into amphetamine in the body. Amphetamine based drugs are also known to reduce food intake. They are addictive substances due to their ability to increase dopamine release. Fenproporex is used as an appetite suppressant, and anti-obesity agent; however, due to substance abuse potential, it is an illicit substance in many countries. In some countries, such as Brazil, it is still prescribed - often in the form of diet pills (Brazilian Diet Pills) which combine amphetamines, benzodiazepines, antidepressants, diuretics and laxatives. In the United States the sale of such diet pills has been banned due to concerns over side effects, and the risk of potentially fatal overdose. However, internet sales and illicit markets has lead to international availability.