Why do some over the counter remedies say only use for 7 days, then consult a doctor? Are they dangerous to use longer than that?

Some medicines contain other medicines that you will become addicted too if you take them for so many days in a row. It happened to me! I bought over the counter paracetamol/codeine. Codeine is an addiction medicine but I didn’t plan on taking it for long... I had a very sore tooth and the box said no more than 3 days at a time. I’d never taken codeine before so I wasn’t to know what addiction would feel like. I took the tablets for 10 days solid and went through 3 boxes of them. When I stopped I felt very poorly and couldn’t sleep and all I could think about was taking more of the pills. I didn’t and I fought it. Thankfully! Also sometimes your problem might be a bigger problem so if it’s not gone within 7 days it’s best to see a dr to see what is actually wrong rather than you just thinking you have pulled a muscle and it actually being a Dvt for example 

It means that the condition they are treating might be more serious if you need to take the drug for longer than a week.

And it does absolve them of liability if you take it longer and something goes wrong.

It is more that if your symptoms persist for that long you need to see a doctor rather than self medicate.

The remedy is designed to relieve symptoms of a short-term illness. If you're still having those symptoms 7 days later, you may have a different type of illness than the one this remedy was designed for and should have a doctor look at it.

(I'm using your example of 7 days. Different remedies have different info.)

Yes, may be .  Or may be not and that's not what your body needs. So the physician has to investigate further