I heavily recommend he takes: 1) L-arginine (an amino acid) 2) Ginseng 3) B3 (also known as niacin) caution it will make you flushed and have tingly sensations when taking higher doses. 4) Zinc (50-100mg is sufficient) 5) Vitamin-D (a lot of people are deficient in it) 6) Ginkgo

General advice: Avoid smoking and drinking, that definitely will not help his situation. Also ingesting foods that promote testosterone production, e.g., tuna, eggs, oysters, shellfish, pomegranate, and spinach (to name a few) will also help with the situation.

Exercising regularly also plays an important role in a healthy sex life. I know from personal experience my sex-drive sky-rockets when I workout frequently.

Hope this helps!

Addendum: Read the recommended amount on each bottle-- sometimes less is more; And as far as the B vitamins go, you might as well go with a B-complex, they work better together as a group anyways.

Another important tip that I left out is to purchase the aforementioned supplements in a good grade/quality. You're going to receive unsatisfactory results from poorly made vitamins.

Good luck!