My Husband Was Prescribed Gabapentin 300 Mg. For Sleep. He

My husband was prescribed Gabapentin 300 mg. for sleep. He wants to know if this medication is safe. Also, he has a history of Seizure Disorder, Not Otherwise Specified, Major Depressive Disorder; Attention Deficit Disorder- Combined Type and diagnosed Sleep Apnea (he uses a Sleep Apnea machine every night) and sees his Pulmonologist regularly. He is currently prescribed and consistently taking: Methylphenidate 36 mg ER x 2 tablets in the AM. He also takes Duloxetine DR 30 mg x 3 capsules in the AM. He also takes Prazosin 1 mg. x 1 to 2 capsules , PM (Minipress) and Tamsulosin, 0.4 mg. 1 capsule in the PM. He has gained an enormous amount of weight since taking past medications for his seizure disorder in the past. He has been seizure free for over 20 years. Is the Gabapentin o.k. for him to take? Is it going to cause him to gain MORE weight? Is this medication going to cause addiction?