There is no definitive answer to this question as it largely depends on the specific Walgreens location and what policies are in place there. Some Walgreens locations may allow you to drop UPS as long as you have a valid prescription, while others may not allow this at all. Additionally, some Walgreens locations may only allow you to drop UPS if you are purchasing them in conjunction with a prescription.
It is important to check with the specific store before making a purchase. In general, though, it seems that dropping UPS at Walgreens is generally allowed, with the exception of some locations that may have specific restrictions.