Ok.... I'll go throught this sequentially so I'll be better able to clarify any pertinant issues.
First, if his liver functions are normal, Tylenol won't cause a problem. If not, Tylenol can be a detriment to his liver.
The main ingredient in the Tylenol PM is diphenhydramine (Benadryl) If this is his first time taking Benadryl, start with one pill and go up from there. Benadryl makes some people sleepy, while others get wired up. Just check with your husband to see which scenario applies ot him.
If he doesn't need the Tylenol for pain, you may want to consider purchasing the Bedadryl (or store brand generic). This will save you some money and eliminate the administration of unnecessary medication. Start with 25 mg, then up to 50mg at bedtime.
One final note, if your husband has been diagnosed or potentiall has Prostate Hypertrophy (excessive size or growth), the problems with his ability to urinate will increase. If he has no problems urinating, he'll be o.k.
Please let me know if I can be of further assistance.
Best Wishes,
LiddyBea