The strongest sleeping pill on the market that you can buy over the counter are Unisom Sleeping pills.
Unisom is what I take over the counter when I cannot sleep and within 30 minutes I'm getting drowsy and about to fall asleep.
So I take the Unisom sleeping pills within 30 minutes before bed and as soon as I get into bed I start to drift off to sleep and I fall asleep and stay asleep the whole night and wake up refreshed.
However if you need any sleeping pill stronger than Unisom you'll need to see your doctor and get a prescription sleeping pill.
Over the counter sleeping pills are good and help some people sleep but sometimes a persons insomnia will be so bad that they need prescription strength sleeping pills.
Ambien is a strong prescription sleeping pill and will help you sleep but since it's prescription you'll need to see your doctor to get it.
Or even Dalmane is a good prescription sleeping pill and there are many others that your doctor can prescribe you.