For the benefit of members:
The active ingredient in Lergigan is called promethazine. A very current, other, brand name is Phenergan.
A usual adult dosage, for allergies, and insomnia, is 25mg once daily at bedtime. Someone willing to stay on the safer side can take 12,5 mg daily at bedtime.
Smaller dosages can be spread throughout the day, like when taken for motion sickness, but taking it during the day is not convenient, and can be hazardous, because of the drowsiness that promethazine induces ( similar to Gravol /dimenhydrinate, for example.)