Antihistamines are common cures for allergies, bites and hayfever. However, they can also provide the drowsiness that is needed for someone to sleep. A positive aspect of these drugs is that they are available at pharmacies, e.g. diphenhydramine, which is commonly used for insomnia. However, medical advice should be sought before taking these drugs. It is also vitally important that you are aware of your drowsiness, and the tablets should not be taken before you are taking on a task that involves concentration, such as driving. Equally, you should monitor any drowsiness felt the day after you have taken these drugs as this could seriously impair your concentration. Antihistamines may also leave you feeling groggy and fatigued in a morning, and this should also be monitored.