I have my doubts, but it appears safe and inexpensive. Walnuts are a good source of omega 3s, so there's that. I'm waiting for a supplement company to start marketing walnut leaf. The news article says:
Looking for a natural way to enhance your fertility, then a daily intake of African Walnuts leaves and nuts may be all you need to solve all these problems. Notably, experts in a new study suggest that African walnut leaves like its nuts also can significantly boost libido or erectile function. It helped boost sperm count and quality. In fact, walnut leaf extract at the highest concentration showed a more pronounced effect than the standard drug in test animals under laboratory conditions. The study which involved Dr Seun Akomolafe at the Ekiti State University, Ado Ekiti and Dr Ganiyu Oboh at the Federal University of Technology, Akure was published in the 2017 edition of the Journal of Complementary Integrated Medicine.