Yes, you can still take Tylenol once it has expired. The law is what requires an expiration date, but it shouldn't do you any harm. It is said that medicines that expire lose their efficiency, but that's neither here nor there. Some will say to take double the does for expired medicine, but since it's known that one can overdose on Tylenol, I would go with the opinion of taking the regular dosage. They do have a 1-800 number if you have anymore concerns. The number is 1-800-962-5357.
i would think it lose it potency, but the tylenol company has issued a recovery of childrens and adults tylenol so it would problely be best to not take it. A good bath can be very relaxing for your mucles and some camomile tea dims your nerves, but do not drive for 4 hours after drinking it, as it can lead to wandering of the mind (AKA daydreaming) and tiredness.