Hello You didn t mention your age and disease for which this drug was advised ? Metpure-XL is a beta blockers metoprolol and it causes sexual dysfunction and impotence ( this is the side effect but this is a minor side effect and it decreases sex but very low )but in your case disease or tension of disease may be responsible for low sexual desire . However to some extent low desire may be due to metoprolol . As it is advised for patient having angina pectoris, hypertension, stable symptomatic heart failure and as adjunct in hyperthyroidism . At present in my opinion don t think about sex matters ( if your age is 50 years ) ,think about the benefits caused by this medicine . Alternatively consult a psychiatrist and get his opinion but before any medicine consult your treating physician as this is most important point in this case. Good luck.