Final answer:
The serotonergic agonist fenfluramine does not have severe stomach cramps as its primary serious side effect when used to treat obesity.
Step-by-step explanation:
The statement that is NOT true of the serotonergic agonists fenfluramine to treat obesity is: Its primary serious side effect is severe stomach cramps.
Fenfluramine is a drug that was used in the past as an appetite suppressant to treat obesity. It stimulates the release of serotonin (5-HT) in the brain, which leads to the suppression of eating and a decrease in appetite. However, one of the main reasons fenfluramine was removed from the market was due to its association with serious side effects, particularly heart valve problems.