I sometimes pop small doses of melatonin (1-2 mg) during months when sunlight is limited, but it's effectiveness
is sometimes called into question. There are natural sources of melatonin that might be a better alternative to the synthetic form.
Living in the north east hemisphere is an absolute challenge for someone with a chronic disease in the winter time. It's terrible actually and 95 percent of us get sick around here because of the hideous weather.
I would just caution against higher doses (5 mg and upwards) and everyday use. It's better to just get 30 min to 1 hour of sunlight when possible and then dim the lights after 6:00 PM.
The pineal gland will downregulate melatonin production if the synthetic form is abused. Conversely, it sometimes needs a boost when production is low (as during the winter time).