While tomatoes are part of the nightshade family, tomato leaves have actually been found to be edible in small quantities. As of 2014, tomato plants are found on the poisonous list, but there is very little evidence that this is true.
Tomato leaves have tomatine in them, which is actually found in a green tomato before it ripens. Fried green tomatoes are an iconic American food and are not considered a dangerous item to consume. In large quantities, the leaves can be toxic, however, so it is advisable not to regularly consume these leaves.
Tomatine has been found to lower LDL cholesterol and help fight cancer. Some ways to consume these leaves is to cook in tomato sauces, brew into teas, eat as fresh young leaves as greens and incorporate into pesto.