Cialis

One of the side effects of Cialis (a drug for the treatment of erectile dysfunction) is stated as "delayed backache".

Hmmm... you've got a 60-yr. old impotent man having sex for the first time in 12 years and you wonder why he may possibly have a backache?!?!?  Must be the drug, right?

Other potential side effects include a dopey grin on your face and an acute awareness of how saggy and flabby your ancient body is.