I don't understand what you're getting at.
Valerian contains unknown psychoactive substances that act as a sedative. Studies show that valerian is arguably effective as a hypnotic and can exhibit withdrawal symptoms similar to those of benzos. Most of the studies published on valerian are either non-scientific or result in insufficient evidence for any positive effects.
Melatonin is an isolated neurohormone that helps to regulate the circadian rhythm and can act as a sedative in higher doses. Melatonin has no addiction potential and only has a few mild side effects, the worst of which is grogginess the morning-after. Melatonin has already had plenty of professional scientific studies proving its' efficacy.
Both are available over the counter just about anywhere. Having read summaries of the drugs, do you understand why doctors suggest melatonin rather than valerian?
You're more of a "consumer whore" for buying and eating a risky herb because of homeopathic jibberjabber than you would be for buying a proven-effective supplement because of pharmacist recommendation.