Which of the following is a known adverse effect of phen-fen?

The association of phen-fen with primary pulmonary hypertension is well-documented and is one of the most serious known adverse effects. Phen-fen is a combination of fenfluramine and phentermine, which was commonly used as a weight-loss treatment. However, studies revealed that the use of fenfluramine contributed to the development of primary pulmonary hypertension, a rare but life-threatening condition characterized by high blood pressure in the blood vessels of the lungs. This condition can lead to heart failure and is associated with substantial morbidity and mortality.

The other options, while they may represent potential side effects or issues related to weight management, do not have the same level of severity or documented association with phen-fen as primary pulmonary hypertension. Understanding this adverse effect is crucial for clinicians who prescribe weight loss medications, as it emphasizes the importance of monitoring patients for serious cardiovascular complications associated with certain anti-obesity treatments.