Melatonin has a half-life of 30-45 minutes. There is evidence to suggest that melatonin is not effective in treating most primary sleep disorders with short-term use (4 weeks or less). Drowsiness is reported as one of the most common side effects of melatonin.
5-HTP is generally converted in the gut to serotonin, where it has a local effect rather than reaching the brain. This increases the risk of gastrointestinal upset. Valerian can interact with prescription medication, and there is very little evidence that GABA given orally can reach the brain, and hence there is little likelihood of it having a positive effect in insomnia.