These are one of the funniest kind of jokes because the Medical profession is otherwise a serious profession.
The old man in his mid-eighties struggles to get up from the couch then starts putting his coat on.

His wife, seeing his unexpected behavior, asks, "And where do you think you are going?"

He replies, "I'm off to the doctor."

She says, "Why, are you sick?"

He says, "Nope, I'm going to get me some of that Viagra stuff."

Hearing this the wife starts struggling to get out of her rocker, she then slowly goes to the cupboard and starts to put on her coat.

The husband now looks mystified and starts to yell at his wife.
He says, "And where on earth do you think you are going?

she answers, "I'm off to the doctor, too."

He says, "Why, what do you need a doctor for?"

She says, "Well if you're going to start using that rusty old thing again, I'm getting a tetanus shot!"