Cimetidine (Tagamet, generic forms): 400 mg twice daily or 800 mg at bedtime
Ranitidine (Zantac, generic forms): 150 mg twice daily or 300 mg at bedtime
Famotidine (Pepcid): 20 mg twice daily or 40 mg at bedtime
Nizatidine (Axid): 150 mg twice daily or 300 mg at bedtime