Which of the following is a proven negative effect of ephedra?

The proven negative effect of ephedra is hypertension, which is a condition characterized by elevated blood pressure. Ephedra, an herbal supplement that contains the stimulant ephedrine, has been shown to increase heart rate and blood pressure in users. This can lead to significant cardiovascular risks, including heart attack and stroke, particularly in individuals with pre-existing health conditions or those who use it in combination with other stimulants. The elevation in blood pressure can cause long-term damage to the cardiovascular system, making hypertension a serious concern for those consuming ephedra.

The other options listed do not represent negative effects of ephedra. Increased eye health and improved mood are not documented effects, while weight stabilization is often not directly attributed to ephedra's use, as its primary association is with weight loss rather than stabilization. Thus, the implications of using ephedra should be carefully considered, particularly regarding the risk of hypertension.