I don't want to take propecia (finasteride)...what natural supplements can i take to help slow hair loss?

There are none: There are no vitamins, herbs, supplements, foods, nor drinks that are proven to slow hair loss (male pattern baldness in men). Maintaining a balanced diet of healthy foods, and taking one multivitamin + minerals tablet each day, should keep a person in normal, good nutritional status . . . So his scalp and hair should be as healthy as they can be. Unusual hair loss should be checked by a doctor.

Topical minoxidil: If you want to avoid oral meds consider topical Minoxidil in 2-5 % strength aka rogaine (minoxidil).